Methods and systems for generating aqueous polymer solutions

ABSTRACT

Provided herein are liquid polymer (LP) compositions comprising a synthetic (co)polymer (e.g., an acrylamide (co)polymer), as well as methods for preparing aqueous polymer solutions by combining these LP compositions with an aqueous fluid. The resulting aqueous polymer solutions can have a concentration of a synthetic (co)polymer (e.g., an acrylamide (co)polymer) of from 50 to 15,000 ppm, and a filter ratio of 1.5 or less at 15 psi using a 1.2 μm filter. Also provided are methods of using these aqueous polymer solutions in oil and gas operations, including enhanced oil recovery.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Patent ApplicationNo. 62/431,255, filed Dec. 7, 2016, which is hereby incorporated hereinby reference in its entirety.

BACKGROUND

Water-soluble polymers, such as polyacrylamide and copolymers ofacrylamide with other monomers, are known to exhibit superior thickeningproperties when said polymers are dissolved in aqueous media.Particularly well-known for this purpose are the anionic carboxamidepolymers such as acrylamide/acrylic acid copolymers, including thoseprepared by hydrolysis of polyacrylamide. Such polymers can be used asfluid mobility control agents in enhanced oil recovery (EOR) processes.

In the past, these polymers were made available commercially as powdersor finely divided solids which were subsequently dissolved in an aqueousmedium at their time of use. Because such dissolution steps aresometimes time consuming and often require rather expensive mixingequipment, such polymers are sometimes provided in water-in-oilemulsions wherein the polymer is dissolved in the dispersed aqueousphase. The water-in-oil emulsions can then be inverted to formoil-in-water emulsions at their time of use. Unfortunately for manyapplications, existing water-in-oil emulsions do not invert as readilyas desired. Furthermore, the resulting inverted emulsions are oftenunable to pass through porous structures. This significantly limitstheir utility as, for example, fluid mobility control agents in EORapplications. In addition, existing water-in-oil emulsions often cannotbe efficiently inverted using an aqueous medium containing dissolvedsalts, as is often the case for enhanced oil recovery practices.

Accordingly, improved methods for preparing aqueous polymer solutionsare needed.

SUMMARY

Provided herein are methods for preparing aqueous polymer solutions.Methods for preparing aqueous polymer solutions can comprise combining aliquid polymer (LP) composition comprising one or more synthetic(co)polymers (e.g., one or more acrylamide (co)polymers) with an aqueousfluid in a single stage mixing process to provide an aqueous polymersolution having a concentration of one or more synthetic (co)polymers(e.g., one or more acrylamide (co)polymers) of from 50 to 15,000 ppm.The single stage mixing process can comprise applying a specific mixingenergy of at least 0.10 kJ/kg (e.g., a specific mixing energy of from0.10 kJ/kg to 1.50 kJ/kg, a specific mixing energy of from 0.15 kJ/kg to1.40 kJ/kg, a specific mixing energy of from 0.15 kJ/kg to 1.20 kJ/kg)to the LP composition and the aqueous fluid. The resulting aqueouspolymer solutions can exhibit a filter ratio of 1.5 or less (e.g., afilter ratio of 1.2, a filter ratio of 1.2 or less, and/or a filterratio of from 1.1 to 1.3) at 15 psi using a 1.2 μm filter.

The LP composition can comprise a variety of suitable LP compositions.In some examples, the LP composition can comprises one or morehydrophobic liquids having a boiling point at least 100° C.; at least39% by weight of the one or more synthetic (co)polymers; one or moreemulsifier surfactants; and one or more inverting surfactants. In otherexamples, the LP composition can be in the form of an inverse emulsioncomprising one or more hydrophobic liquids having a boiling point atleast 100° C.; up to 38% by weight of one or more synthetic(co)polymers; one or more emulsifier surfactants; and one or moreinverting surfactants. In still other examples, the LP composition cancomprise a substantially anhydrous polymer suspension comprising apowder polymer having an average molecular weight of from 0.5 to 30million Daltons suspended in a carrier having an HLB of greater than orequal to 8. In these embodiments, the carrier can comprise one or moresurfactants. In these embodiments, the powder polymer and the carriercan be present in the substantially anhydrous polymer suspension at aweight ratio of from 20:80 to 80:20.

In some embodiments, the single stage mixing process can comprise asingle mixing step. The single mixing step can comprise, for example,passing the LP polymer composition and the aqueous fluid through anin-line mixer having a mixer inlet and a mixer outlet to provide theaqueous polymer solution. The in-line mixer can be a static mixer or adynamic mixer (e.g., an electrical submersible pump, a hydraulicsubmersible pump, or a progressive cavity pump). The in-line mixer canbe positioned on the surface, subsurface, subsea, or downhole.

In other embodiments, the single stage mixing process can comprise amultiple mixing step. For example, in some cases, the single stagemixing process can comprise as a first mixing step, passing the LPpolymer composition and the aqueous fluid through a first in-line mixerhaving a first mixer inlet and a first mixer outlet to provide apartially mixed aqueous polymer solution; and as a second step, passingthe partially mixed aqueous polymer solution through a second in-linemixer having a second mixer inlet and a second mixer outlet to providethe aqueous polymer solution. The first in-line mixer and the secondin-line mixer can each individually be a static mixer or a dynamic mixer(e.g., an electrical submersible pump, a hydraulic submersible pump, ora progressive cavity pump). In some cases, the first in-line mixer cancomprise a dynamic mixer and the second in-line mixer can comprise astatic mixer. In some cases, the first in-line mixer can comprise astatic mixer and the second in-line mixer can comprise a dynamic mixer.In other cases, both the first in-line mixer and the second in-linemixer can comprise a dynamic mixer.

In other embodiments, the single stage mixing process can compriseparallel single mixing steps. The parallel single mixing steps cancomprise combining the LP composition with an aqueous fluid in a polymermixing system. In certain embodiments, the polymer mixing system can bepositioned subsea. The polymer mixing system can comprise a main polymerfeed line diverging to a plurality of polymer supply branches, a mainaqueous feed line diverging to a plurality of aqueous supply branches,and a plurality of mixer arrangements, each of which comprises anin-line mixer having a mixer inlet and a mixer outlet. Each of theplurality of mixer arrangements in the polymer mixing system is suppliedby one of the plurality of polymer supply branches and one of theplurality of aqueous supply branches. In some variations, the mainpolymer feed can be fluidly connected to the plurality of polymer supplybranches via a polymer distribution manifold. Optionally, the polymerdistribution manifold can independently control the fluid flow ratethrough each of the plurality of polymer supply branches.

Optionally, the mixing system can further comprise a flow control valveoperably coupled to each the plurality of polymer supply branches tocontrol fluid flow rate through each of the plurality of polymer supplybranches. Optionally, the mixing system can further comprise a flowcontrol valve operably coupled to each the plurality of aqueous supplybranches to control fluid flow rate through each of the plurality ofaqueous supply branches. In certain embodiments, the mixing system canfurther comprise a flow control valve operably coupled to each theplurality of polymer supply branches to control fluid flow rate througheach of the plurality of polymer supply branches, and a flow controlvalve operably coupled to each the plurality of aqueous supply branchesto control fluid flow rate through each of the plurality of aqueoussupply branches. Examples of suitable flow control valves include, forexample, choke valves, chemical injection metering valves (CIMVs), andcontrol valves.

The LP composition and the aqueous fluid can be combined in the polymermixing system by passing the LP polymer composition through the mainpolymer feed line and the plurality of polymer supply branches to reacheach of the plurality of mixer arrangements. The LP polymer compositionand the aqueous fluid can then flow through the in-line mixer of each ofthe plurality of mixer arrangements to provide a stream of the aqueouspolymer solution.

In other embodiments, the single stage mixing process can compriseparallel multiple mixing steps. The parallel multiple mixing steps cancomprise combining the LP composition with an aqueous fluid in a polymermixing system. In certain embodiments, the polymer mixing system can bepositioned subsea. The polymer mixing system can comprise a main polymerfeed line diverging to a plurality of polymer supply branches, a mainaqueous feed line diverging to a plurality of aqueous supply branches,and a plurality of mixer arrangements. In some variants, the mainpolymer feed line can be fluidly connected to the plurality of polymersupply branches via a polymer distribution manifold. The polymerdistribution manifold can be configured to independently control thefluid flow rate through each of the plurality of polymer supplybranches. Each of the plurality of mixer arrangements in the mixingsystem is supplied by one of the plurality of polymer supply branchesand one of the plurality of aqueous supply branches. Each of theplurality of mixer arrangements can comprise a first in-line mixerhaving a first mixer inlet and a first mixer outlet in series with asecond in-line mixer having a second mixer inlet and a second mixeroutlet.

Optionally, the mixing system can further comprise a flow control valveoperably coupled to each the plurality of polymer supply branches tocontrol fluid flow rate through each of the plurality of polymer supplybranches. Optionally, the mixing system can further comprise a flowcontrol valve operably coupled to each the plurality of aqueous supplybranches to control fluid flow rate through each of the plurality ofaqueous supply branches. In certain embodiments, the mixing system canfurther comprise a flow control valve operably coupled to each theplurality of polymer supply branches to control fluid flow rate througheach of the plurality of polymer supply branches, and a flow controlvalve operably coupled to each the plurality of aqueous supply branchesto control fluid flow rate through each of the plurality of aqueoussupply branches. Examples of suitable flow control valves include, forexample, choke valves, chemical injection metering valves (CIMVs), andcontrol valves.

The LP composition and the aqueous fluid can be combined in the polymermixing system by passing the LP polymer composition through the mainpolymer feed line and the plurality of polymer supply branches to reacheach of the plurality of mixer arrangements. The LP polymer compositionand the aqueous fluid can then flow through the through a first in-linemixer having a first mixer inlet and a first mixer outlet, emerging as astream of partially mixed aqueous polymer solution. The partially mixedaqueous polymer solution can comprise a concentration of synthetic(co)copolymer of from 50 to 15,000 ppm (e.g., from 500 to 5000 ppm, orfrom 500 to 3000 ppm). The stream of partially mixed aqueous polymersolution can then pass through a second in-line mixer having a secondmixer inlet and a second mixer outlet, emerging as a stream of aqueouspolymer solution.

Also provided herein are method for hydrocarbon recovery. The methodsfor hydrocarbon recovery can comprise providing a subsurface reservoircontaining hydrocarbons there within; providing a wellbore in fluidcommunication with the subsurface reservoir; preparing an aqueouspolymer solution according to the methods described herein; andinjecting the aqueous polymer solution through the wellbore into thesubsurface reservoir. The wellbore in the second step can be aninjection wellbore associated with an injection well, and the method canfurther comprise providing a production well spaced apart from theinjection well a predetermined distance and having a production wellborein fluid communication with the subsurface reservoir. In theseembodiments, injection of the aqueous polymer solution can increase theflow of hydrocarbons to the production wellbore. In some embodiments,the wellbore in the second step can be a wellbore for hydraulicfracturing that is in fluid communication with the subsurface reservoir.

DESCRIPTION OF DRAWINGS

FIG. 1 is a process flow diagram schematically illustrating an examplesingle stage mixing process for preparing an aqueous polymer solution.The example single stage mixing process comprises a single mixing step.

FIG. 2 is a process flow diagram schematically illustrating an examplesingle stage mixing process for preparing an aqueous polymer solution.The example single stage mixing process comprises a two mixing steps.

FIG. 3 is a process flow diagrams schematically illustrating an examplesingle stage mixing process for preparing an aqueous polymer solution.The example single stage mixing process comprises a plurality ofparallel mixing steps (e.g., parallel single mixing steps, parallelmultiple mixing steps, or a combination thereof).

FIGS. 4A and 4B are process flow diagrams schematically illustratingexample single stage mixing processes for preparing an aqueous polymersolution that comprise parallel single mixing steps carried out in apolymer mixing system (e.g., a subsea polymer mixing system).

FIGS. 5A and 5B are process flow diagrams schematically illustratingexample single stage mixing processes for preparing an aqueous polymersolution that comprise parallel multiple mixing steps carried out in apolymer mixing system (e.g., a subsea polymer mixing system).

FIG. 6 is a plot of the pressure drop and relative permeability uponinjection of an inverted polymer solution in a sandstone core. Thesteady pressure drop and steady relative permeability observed uponinjection of the inverted polymer solution are consistent with noplugging of the sandstone core.

FIG. 7 is a plot of the filtration ratio test performed using a 1.2micron filter for an inverted polymer solution. The inverted polymersolution (2000 ppm polymer) passes through 1.2 micron filter with afilter ratio of less than 1.2, which shows improved filterability of theinverted polymer solution.

FIG. 8 is a viscosity plot in the wide range of shear rate for aninverted polymer solution (2000 ppm polymer in synthetic brine, measuredat 31° C.). The viscosity of the inverted polymer solution shows atypical shear-thinning behavior in the wide range of shear rate. Theviscosity is measured as 24 cP at 10 s-1 and 31° C.

FIG. 9 is a viscosity plot in the wide range of shear rate for neat LPcomposition activity of the neat LP composition test here is 50% and theviscosity of LP is measured at 180 cP at 10 s⁻¹ and 25° C. Low viscositywith high activity makes the LP composition easy to handle in the field.

FIG. 10 is an oil recovery and pressure drop plot for an inverted LPsolution (2000 ppm polymer) in unconsolidated-sand pack. Oil recoveryincreases as the inverted LP is injected while pressure drop for LPinjection shows steady-state and low at the end of the experiment. Thesteady-state low pressure drop from LP at the end of the experimentindicates improved behavior as the LP solutions do not plug the coreduring oil recovery.

FIG. 11 is a plot showing the LP viscosity as a function ofconcentration at a temperature of 31° C. and shear rate of 10 sec⁻¹.

FIG. 12 is a plot of LP shear viscosities as a function of shear rate ata temperature of 31° C.

FIGS. 13A and 13B are plots of filtration ratio tests performed using a5 micron filter (FIG. 13A) and 1.2 micron filter (FIG. 13B) for invertedpolymer solutions M1-M6. The inverted polymer solution (2000 ppmpolymer) passes through 1.2 micron filter with a filter ratio of lessthan 1.5, which shows improved filterability of the inverted polymersolution.

FIG. 14 is a plot of the pressure drop upon injection of an invertedpolymer solution (2000 ppm) in a sandstone core (1.2 D) with a pressuretab attached at 2″ from the inlet to monitor face plugging. The steadypressure drop observed upon injection of the inverted polymer solutionin both whole and 1^(st) section in the core are consistent with nosignificant plugging of the sandstone core. The inverted polymer wasinjected up to 45 PV followed by post-water flood. The pressure dropduring the post-water flood also showed that injection of the invertedpolymer solution did not plug the core.

FIG. 15A is a plot of the normalized permeability reduction of aninverted conventional liquid polymer LP#1 (2000 ppm) in a sandstone witha pressure tap (3″) showing face plugging at the inlet. FIG. 15B is aplot of the normalized permeability reduction of the inverted LPcomposition (2000 ppm) in a sandstone with a pressure tap (2″) showingno significant plugging above 250 PV of injection at inlet.

FIG. 16 is a plot of the Permeability Reduction Factor (R_(k)) andNormalized Skin Factor, s/ln(r_(s)/r_(w)) as a function of thefiltration ratio at 1.2 μm (FR_(1.2)). R_(k) and skin factor werecalculated at 25 PV of injection into sandstone core.

FIG. 17 is a bar graph illustrating the viscosity yield achieving usingmulti-step (two) mixing configurations and single step mixingconfigurations with and without a dynamic mixer.

FIG. 18A is a plot of the viscosity yield as a function of the pressuredrop across the static mixer(s).

FIG. 18B is a plot of the filtration ration as a function of thepressure drop across the static mixer(s).

FIG. 19 is a process flow diagram schematically illustrating traditionaltwo-stage mixing processes used to prepare aqueous polymer solutionsfrom LP compositions.

FIG. 20 is a process flow diagram schematically illustrating a singlestage mixing processes used to prepare aqueous polymer solutions from LPcompositions.

FIG. 21 is a schematic illustration of the internal elements of the 6″SCH 120 static in-line Sulzer SMX mixer.

FIG. 22 is a plot showing the average viscosity yield across a10,000-30,000 bpd flow rate range associated with various yard-scalemixer configurations.

FIG. 23 is a plot showing the variation of pressure drop (DP) andfiltration ratio (FR) as a function of injection rate using the mixerconfiguration shown in FIG. 2 at 2″ yard test scale. Dotted linesindicate the DP across the static mixer with and without the dynamicmixer. Solids symbols indicate the filtration ratio of the aqueouspolymer solutions at each corresponding injection rates. Filtrationratio was measured using 1.2 micron filter under 15 psi.

FIG. 24 is a plot showing the correlation between yard test and fieldscale DP as a function of fluid velocity.

FIG. 25 is a plot showing the correlation between yard test and fieldscale FR as a function of DP.

FIG. 26A is a plot of filtration ratio as a function of specific mixingenergy for various single stage mixing configurations employing in-linestatic mixers in yard tests and field scale pilot tests.

FIG. 26B is a plot of filtration ratio as a function of specific mixingenergy for various single stage mixing configurations employing in-linestatic mixers in yard tests and lab scale overhead mixing tests.

FIG. 27 is a plot of viscosity as a function of mixing energy for singlestage and dual stage mixing configurations employing in-line staticmixers.

FIG. 28 is a plot of a field core flood (CF1) performed using theaqueous polymer solution in laboratory. Polymer was prepared in the labusing field neat liquid polymer. The polymer flood was run at 0.5 ml/minin the sandstone (1.4 D)

FIG. 29 is a plot of a field core flood (CF2) performed using aqueouspolymer solution obtained from the wellhead. The LP composition wasinverted using a single stage in-line mixer in the field, and a sampleof the aqueous polymer solution was obtained from the wellhead. Thepolymer flood was run at 0.5 ml/min in the sandstone (1.4 D).

FIG. 30 shows the results of a filtration ratio test performed usingsamples of 1800 ppm aqueous polymer solution obtained from the wellhead.The filtration ratio test was performed using a 1.2 micron filter at 1bar.

FIG. 31 is a plot of capillary viscosity measurements from an offshorefield application showing the effect of changes in flow rate on coilviscometer measurements sampled from the wellhead. To estimate theviscosity of samples, pressure drop was measured through coil tubing onthe core flood apparatus and data.

FIG. 32 is a plot showing the Darcy-Weisbach relation in a single stageinline mixer. The plot shows the correlation between pressure drop andflow rate, and the slope indicates the Darcy friction factor in thegiven system.

FIG. 33 is a plot of the Darcy friction factor vs. Reynolds number for2″D and 3″D single step inline mixers. The Darcy friction factor insmooth pipe flow is marked as baseline.

FIG. 34A is a plot of the specific mixing energy (SME) vs filtrationratio with powder HPAM polymer solution using a 5 micron filter.

FIG. 34B is a plot of the specific mixing energy (SME) vs. filtrationratio with powder HPAM polymer solution using a 1.2 micron filter.

FIG. 35 is a plot of the specific mixing energy (SME) vs. viscosity withpowder HPAM polymer solution: 1000 ppm polymer in synthetic seawater

FIG. 36A is a sensitivity test performed using a powder polymersolution. Filtration ratio is plotted as a function of mixing speed.

FIG. 36B is a sensitivity test performed using a powder polymersolution. Filtration ratio is plotted as a function of mixing hydrationtime.

FIG. 37 is a schematic illustration of an example subsea polymer mixingsystem.

FIG. 38 is a schematic illustration of an example subsea polymer mixingsystem.

DETAILED DESCRIPTION

Provided herein are methods for preparing aqueous polymer solutions thatcomprise combining a liquid polymer (LP) composition with an aqueousfluid in a single stage mixing process. Also provided are methods ofusing these aqueous polymer solutions in oil and gas operations,including enhanced oil recovery (EOR).

The term “enhanced oil recovery” refers to techniques for increasing theamount of unrefined petroleum (e.g., crude oil) that may be extractedfrom an oil reservoir (e.g., an oil field). Using EOR, 40-60% of thereservoir's original oil can typically be extracted compared with only20-40% using primary and secondary recovery (e.g., by water injection ornatural gas injection). Enhanced oil recovery may also be referred to asimproved oil recovery or tertiary oil recovery (as opposed to primaryand secondary oil recovery). Examples of EOR operations include, forexample, miscible gas injection (which includes, for example, carbondioxide flooding), chemical injection (sometimes referred to as chemicalenhanced oil recovery (CEOR), and which includes, for example, polymerflooding, alkaline flooding, surfactant flooding, conformance controloperations, as well as combinations thereof such as alkaline-polymerflooding or alkaline-surfactant-polymer flooding), microbial injection,and thermal recovery (which includes, for example, cyclic steam, steamflooding, and fire flooding). In some embodiments, the EOR operation caninclude a polymer (P) flooding operation, an alkaline-polymer (AP)flooding operation, a surfactant-polymer (SP) flooding operation, analkaline-surfactant-polymer (ASP) flooding operation, a conformancecontrol operation, or any combination thereof. The terms “operation” and“application” may be used interchangeability herein, as in EORoperations or EOR applications.

For purposes of this disclosure, including the claims, the filter ratio(FR) can be determined using a 1.2 micron filter at 15 psi (plus orminus 10% of 15 psi) at ambient temperature (e.g., 25° C.). The 1.2micron filter can have a diameter of 47 mm or 90 mm, and the filterratio can be calculated as the ratio of the time for 180 to 200 ml ofthe inverted polymer solution to filter divided by the time for 60 to 80ml of the inverted polymer solution to filter.

${FR} = \frac{{{\,^{t}200}\mspace{14mu}{ml}} - {{\,^{t}180}\mspace{14mu}{ml}}}{{{\,^{t}80}\mspace{14mu}{ml}} - {{\,^{t}60}\mspace{14mu}{ml}}}$For purposes of this disclosure, including the claims, the invertedpolymer solution is required to exhibit a FR of 1.5 or less.

The formation of aqueous polymer solutions from a LP composition (e.g.,by inversion of an LP composition such as an inverse emulsion polymer)can be challenging. For use in many applications, rapid and completeinversion of the inverse emulsion polymer composition is required. Forexample, for many applications, rapid and continuous inversion anddissolution (e.g., complete inversion and dissolution in five minutes orless) is required. For certain applications, including many oil and gasapplications, it can be desirable to completely form an aqueous polymersolution (e.g., to invert and dissolve the emulsion or LP to a finalconcentration of from 500 to 5000 ppm) in an in-line system in a shortperiod of time (e.g., less than five minutes).

For certain applications, including many enhanced oil recovery (EOR)applications, it can be desirable that the aqueous polymer solutionflows through a hydrocarbon-bearing formation without plugging theformation. Plugging the formation can slow or inhibit oil production.This is an especially large concern in the case of hydrocarbon-bearingformations that have a relatively low permeability prior to tertiary oilrecovery.

One test commonly used to determine performance of an aqueous polymersolution in such conditions involves measuring the time taken for givenvolumes/concentrations of solution to flow through a filter, commonlycalled a filtration quotient or Filter Ratio (“FR”). For example, U.S.Pat. No. 8,383,560 describes a filter ratio test method which measuresthe time taken by given volumes of a solution containing 1000 ppm ofactive polymer to flow through a filter. The solution is contained in acell pressurized to 2 bars and the filter has a diameter of 47 mm and apore size of 5 microns. The times required to obtain 100 ml (t100 ml),200 ml (t200 ml), and 300 ml (t300 ml) of filtrate were measured. Thesevalues were used to calculate the FR, expressed by the formula below:

${FR} = \frac{{{\,^{t}300}\mspace{14mu}{ml}} - {{\,^{t}200}\mspace{14mu}{ml}}}{{{\,^{t}200}\mspace{14mu}{ml}} - {{\,^{t}100}\mspace{14mu}{ml}}}$

The FR generally represents the capacity of the polymer solution to plugthe filter for two equivalent consecutive volumes. Generally, a lower FRindicates better performance. U.S. Pat. No. 8,383,560, which isincorporated herein by reference, explains that a desirable FR usingthis method is less than 1.5.

However, polymer compositions that provide desirable results using thistest method, have not necessarily provided acceptable performance in thefield. In particular, many polymers that have an FR (using a 5 micronfilter) lower than 1.5 exhibit poor injectivity—i.e., when injected intoa formation, they tend to plug the formation, slowing or inhibiting oilproduction. A modified filter ratio test method using a smaller poresize (i.e., the same filter ratio test method except that the filterabove is replaced with a filter having a diameter of 47 mm and a poresize of 1.2 microns) and lower pressure (15 psi) provides a betterscreening method.

The methods described herein can produce aqueous polymer solutionsexhibiting a FR using the 1.2 micron filter of 1.5 or less via efficientsingle stage mixing processes. In field testing, these compositions canexhibit improved injectivity over commercially-available polymercompositions—including other polymer compositions having an FR (using a5 micron filter) of less than 1.5. As such, the aqueous polymersolutions prepared by the methods described herein are suitable for usein a variety of oil and gas applications, including EOR.

LP Compositions

As discussed above, provided herein are methods for preparing aqueouspolymer solutions that comprise combining a liquid polymer (LP)composition with an aqueous fluid in a single stage mixing process. Themethods described herein can be used in conjunction with a variety ofsuitable LP compositions. Herein, the term “liquid polymer (LP)composition” is used to broadly refer to polymer compositions that arepumpable and/or flowable, so as to be compatible with the single stagemixing processes described herein.

In some examples, the LP composition can comprise a substantiallyanhydrous polymer suspension that comprises a powder polymer having anaverage molecular weight of 0.5 to 30 million Daltons suspended in acarrier having an HLB of greater than or equal to 8. In these polymersuspensions, the powder polymer and the carrier can be present in thesubstantially anhydrous polymer suspension at a weight ratio of from20:80 to 80:20 (e.g., at a weight ratio of from 30:70 to 70:30, or at aweight ratio of from 40:60 to 60:40). The carrier can comprise at leastone surfactant. In some cases, the carrier can be water soluble. In somecases, the carrier can be water soluble and oil soluble.

LP compositions of this type are known in the art, and are discussed inmore detailed in the following cases having Chevron U.S.A. Inc. as anassignee: U.S. Patent Application Publication Nos. 2016/0122622,2016/0122623, 2016/0122624, and 2016/0122626, each of which isincorporated herein by reference in its entirety. Other suitable LPcompositions include compositions described, for example, in SPE 179657entitled “Permeability Reduction Due to use of Liquid Polymers andDevelopment of Remediation Options” by Dwarakanath et al. (SPE IORsymposium at Tulsa 2016), which is incorporated herein by reference inits entirety.

In some of these embodiments, the powder polymer for use in thesuspension is selected or tailored according to the characteristics ofthe reservoir for EOR treatment such as permeability, temperature andsalinity. Examples of suitable powder polymers include biopolymers suchas polysaccharides. For example, polysaccharides can be xanthan gum,scleroglucan, guar gum, a mixture thereof (e.g., any modificationsthereof such as a modified chain), etc. Indeed, the terminology“mixtures thereof” or “combinations thereof” can include “modificationsthereof” herein. Examples of suitable powder synthetic polymers includepolyacrylamides. Examples of suitable powder polymers include syntheticpolymers such as partially hydrolyzed polyacrylamides (HPAMs or PHPAs)and hydrophobically-modified associative polymers (APs). Also includedare co-polymers of polyacrylamide (PAM) and one or both of 2-acrylamido2-methylpropane sulfonic acid (and/or sodium salt) commonly referred toas AMPS (also more generally known as acrylamido tertiobutyl sulfonicacid or ATBS), N-vinyl pyrrolidone (NVP), and the NVP-based syntheticmay be single-, co-, or ter-polymers. In one embodiment, the powdersynthetic polymer is polyacrylic acid (PAA). In one embodiment, thepowder synthetic polymer is polyvinyl alcohol (PVA). Copolymers may bemade of any combination or mixture above, for example, a combination ofNVP and ATB S.

In some embodiments, the carrier can comprise a mixture of surfactants(e.g., a surfactant and one or more co-surfactants, such as a mixture ofnon-ionic and anionic surfactants). Examples suitable surfactantsinclude ethoxylated surfactants, nonylphenol ethoxylates, alcoholethoxylates, internal olefin sulfonates, isomerized olefin sulfonates,alkyl aryl sulfonates, medium alcohol (C10 to C17) alkoxy sulfates,alcohol ether [alkoxy]carboxylates, alcohol ether [alkoxy]sulfates,alkyl sulfonate, α-olefin sulfonates (AOS), dihexyl sulfosuccinates,alkylpolyalkoxy sulfates, sulfonated amphoteric surfactants, andmixtures thereof.

In some embodiments, the carrier can further comprise a co-solvent(e.g., an alcohol, a glycol ether, or a combination thereof). In somecases, the co-solvent can comprise an alcohol ethoxylate (-EO-); analcohol alkoxylate (-PO-EO-); an alkyl polyglycol ether; an alkylphenoxy ethoxylate; an ethylene glycol butyl ether (EGBE); a diethyleneglycol butyl ether (DGBE); a triethylene glycol butyl ether (TGBE); apolyoxyethylene nonylphenylether, or a mixture thereof. In some cases,the co-solvent can comprise an alcohol selected from the group ofisopropyl alcohol (IPA), isobutyl alcohol (IBA) and secondary butylalcohol (SBA).

In some embodiments, the carrier can comprise an ionic surfactant,non-ionic surfactant, anionic surfactant, cationic surfactant,amphoteric surfactant, ketones, esters, ethers, glycol ethers, glycolether esters, lactams, cyclic ureas, alcohols, aromatic hydrocarbons,aliphatic hydrocarbons, alicyclic hydrocarbons, nitroalkanes,unsaturated hydrocarbons, halocarbons, alkyl aryl sulfonates (AAS),a-olefin sulfonates (AOS), internal olefin sulfonates (IOS), alcoholether sulfates derived from propoxylated Ci₂-C₂o alcohols, ethoxylatedalcohols, mixtures of an alcohol and an ethoxylated alcohol, mixtures ofanionic and cationic surfactants, disulfonated surfactants, aromaticether polysulfonates, isomerized olefin sulfonates, alkyl arylsulfonates, medium alcohol (C10 to C17) alkoxy sulfates, alcohol ether[alkoxy]carboxylates, alcohol ether [alkoxy]sulfates, primary amines,secondary amines, tertiary amines, quaternary ammonium cations, cationicsurfactants that are linked to a terminal sulfonate or carboxylategroup, alkyl aryl alkoxy alcohols, alkyl alkoxy alcohols, alkylalkoxylated esters, alkyl polyglycosides, alkoxy ethoxyethanolcompounds, isobutoxy ethoxyethanol (“iBDGE”), n-pentoxy ethoxyethanol(“n-PDGE”), 2-methylbutoxy ethoxyethanol (“2-MBDGE”), methylbutoxyethoxyethanol (“3-MBDGE”), (3,3-dimethylbutoxy ethoxyethanol(“3,3-DMBDGE”), cyclohexylmethyleneoxy ethoxyethanol (hereafter“CHMDGE”), 4-Methylpent-2-oxy ethoxyethanol (“MIBCDGE”), n-hexoxyethoxyethanol (hereafter “n-HDGE”), 4-methylpentoxy ethoxyethanol(“4-MPDGE”), butoxy ethanol, propoxy ethanol, hexoxy ethanol,isoproproxy 2-propanol, butoxy 2-propanol, propoxy 2-propanol, tertiarybutoxy 2-propanol, ethoxy ethanol, butoxy ethoxy ethanol, propoxy ethoxyethanol, hexoxy ethoxy ethanol, methoxy ethanol, methoxy 2-propanol andethoxy ethanol, n-methyl-2-pyrrolidone, dimethyl ethylene urea, andmixtures thereof.

“Substantially anhydrous” as used herein refers to a polymer suspensionwhich contains only a trace amount of water. Trace amount means nodetectable amount of water in one embodiment; less than or equal to 3wt. % water in another embodiment; and containing less than or equal toany of 2.5%, 2%, 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%,0.1%, 0.05% or 0.01% water in various embodiments. A reference to“polymer suspension” refers to a substantially anhydrous polymersuspension.

In other examples, LP compositions can comprise one or more synthetic(co)polymers (e.g., one or more acrylamide (co)polymers) dispersed oremulsified in one or more hydrophobic liquids. In some embodiments, theLP compositions can further comprise one or more emulsifying surfactantsand one or more inverting surfactants. In some embodiments, the LPcompositions can further comprise a small amount of water. For example,the LP compositions can further comprise less than 10% by weight (e.g.,less than 5% by weight, less than 4% by weight, less than 3% by weight,less than 2.5% by weight, less than 2% by weight, or less than 1% byweight) water, based on the total weight of all the components of the LPcomposition. In certain embodiments, the LP compositions can bewater-free or substantially water-free (i.e., the composition caninclude less than 0.5% by weight water, based on the total weight of thecomposition). The LP compositions can optionally include one or moreadditional components which do not substantially diminish the desiredperformance or activity of the composition. It will be understood by aperson having ordinary skill in the art how to appropriately formulatethe LP composition to provide necessary or desired features orproperties.

In some embodiments, the LP composition can comprise one or morehydrophobic liquids having a boiling point at least 100° C.; at least39% by weight of one or more synthetic co-polymers (e.g.,acrylamide-(co)polymers); one or more emulsifier surfactants; and one ormore inverting surfactants.

In some embodiments, the LP composition can comprise one or morehydrophobic liquids having a boiling point at least 100° C.; at least39% by weight of particles of one or more acrylamide-(co)polymers; oneor more emulsifier surfactants; and one or more inverting surfactants.In certain embodiments, when the composition is fully inverted in anaqueous fluid, the composition affords an aqueous polymer solutionhaving a filter ratio (FR) (1.2 micron filter) of 1.5 or less. Incertain embodiments, the aqueous polymer solution can comprise from 500to 5000 ppm (e.g., from 500 to 3000 ppm) active polymer, and have aviscosity of at least 20 cP at 30° C.

In some embodiments, the LP compositions can comprise less than 10% byweight (e.g., less than 7% by weight, less than 5% by weight, less than4% by weight, less than 3% by weight, less than 2.5% by weight, lessthan 2% by weight, or less than 1% by weight) water prior to combinationwith the aqueous fluid, based on the total weight of all the componentsof the LP composition. In certain embodiments, the LP composition, priorto combination with the aqueous fluid, comprises from 1% to 10% water byweight, or from 1% to 5% water by weight, based on the total amount ofall components of the composition.

In some embodiments, the solution viscosity (SV) of a 0.1% solution ofthe LP composition can be greater than 3.0 cP, or greater than 5 cP, orgreater than 7 cP. The SV of the LP composition can be selected based,at least in part, on the intended actives concentration of the aqueouspolymer solution, to provide desired performance characteristics in theaqueous polymer solution. For example, in certain embodiments, where theaqueous polymer solution is intended to have an actives concentration ofabout 2000 ppm, it is desirable that the SV of a 0.1% solution of the LPcomposition is in the range of from 7.0 to 8.6, because at this level,the aqueous polymer solution has desired FR1.2 and viscosity properties.A liquid polymer composition with a lower or higher SV range may stillprovide desirable results, but may require changing the activesconcentration of the aqueous polymer solution to achieve desired FR1.2and viscosity properties. For example, if the liquid polymer compositionhas a lower SV range, it may be desirable to increase the activesconcentration of the aqueous polymer solution.

In some embodiments, the LP composition can comprise one or moresynthetic (co)polymers (e.g., one or more acrylamide (co)polymers)dispersed in one or more hydrophobic liquids. In these embodiments, theLP composition can comprise at least 39% polymer by weight (e.g., atleast 40% by weight, at least 45% by weight, at least 50% by weight, atleast 55% by weight, at least 60% by weight, at least 65% by weight, atleast 70% by weight, or at least 75% by weight), based on the totalamount of all components of the composition. In some embodiments, the LPcomposition can comprise 80% by weight or less polymer (e.g., 75% byweight or less, 70% by weight or less, 65% by weight or less, 60% byweight or less, 55% by weight or less, 50% by weight or less, 45% byweight or less, or 40% by weight or less), based on the total amount ofall components of the composition.

The these embodiments, the LP composition can comprise an amount ofpolymer ranging from any of the minimum values described above to any ofthe maximum values described above. For example, in some embodiments,the LP composition can comprise from 39% to 80% by weight polymer (e.g.,from 39% to 60% by weight polymer, or from 39% to 50% by weightpolymer), based on the total weight of the composition.

In some embodiments, the LP composition can comprise one or moresynthetic (co)polymers (e.g., one or more acrylamide (co)polymers)emulsified in one or more hydrophobic liquids. In these embodiments, theLP composition can comprise at least 10% polymer by weight (e.g., atleast 15% by weight, at least 20% by weight, at least 25% by weight, orat least 30% by weight), based on the total amount of all components ofthe composition. In some embodiments, the LP composition can compriseless than 38% by weight polymer (e.g., less than 35% by weight, lessthan 30% by weight, less than 25% by weight, less than 20% by weight, orless than 15% by weight), based on the total amount of all components ofthe composition.

The these embodiments, the LP composition can comprise an amount ofpolymer ranging from any of the minimum values described above to any ofthe maximum values described above. For example, in some embodiments,the LP composition can comprise from 10% to 38% by weight polymer (e.g.,from 10% to 35% by weight polymer, from 15% to 30% by weight polymer,from 15% to 35% by weight polymer, from 15% to 38% by weight polymer,from 20% to 30% by weight polymer, from 20% to 35% by weight polymer, orfrom 20% to 38% by weight polymer), based on the total weight of thecomposition.

Hydrophobic Liquid

In some embodiments, the LP composition can include one or morehydrophobic liquids. In some cases, the one or more hydrophobic liquidscan be organic hydrophobic liquids. In some embodiments, the one or morehydrophobic liquids each have a boiling point at least 100° C. (e.g., atleast 135° C., or at least 180° C.). If the organic liquid has a boilingrange, the term “boiling point” refers to the lower limit of the boilingrange.

In some embodiments, the one or more hydrophobic liquids can bealiphatic hydrocarbons, aromatic hydrocarbons, or mixtures thereof.Examples of hydrophobic liquids include but are not limited towater-immiscible solvents, such as paraffin hydrocarbons, naphthenehydrocarbons, aromatic hydrocarbons, olefins, oils, stabilizingsurfactants, and mixtures thereof. The paraffin hydrocarbons can besaturated, linear, or branched paraffin hydrocarbons. Examples ofsuitable aromatic hydrocarbons include, but are not limited to, tolueneand xylene. In certain embodiments, the hydrophobic liquid can comprisean oil, for example, a vegetable oil, such as soybean oil, rapeseed oil,canola oil, or a combination thereof, and any other oil produced fromthe seed of any of several varieties of the rape plant.

In some embodiments, the amount of the one or more hydrophobic liquidsin the inverse emulsion or LP composition is from 20% to 60%, from 25%to 54%, or from 35% to 54% by weight, based on the total amount of allcomponents of the LP composition.

Synthetic (Co)Polymers

In some embodiments, the LP composition includes one or more synthetic(co)polymers, such as one or more acrylamide containing (co)polymers. Asused herein, the terms “polymer,” “polymers,” “polymeric,” and similarterms are used in their ordinary sense as understood by one skilled inthe art, and thus may be used herein to refer to or describe a largemolecule (or group of such molecules) that contains recurring units.Polymers may be formed in various ways, including by polymerizingmonomers and/or by chemically modifying one or more recurring units of aprecursor polymer. A polymer may be a “homopolymer” comprisingsubstantially identical recurring units formed by, e.g., polymerizing aparticular monomer. A polymer may also be a “copolymer” comprising twoor more different recurring units formed by, e.g., copolymerizing two ormore different monomers, and/or by chemically modifying one or morerecurring units of a precursor polymer. The term “terpolymer” may beused herein to refer to polymers containing three or more differentrecurring units. The term “polymer” as used herein is intended toinclude both the acid form of the polymer as well as its various salts.

In some embodiments, the one or more synthetic (co)polymers can be apolymer useful for enhanced oil recovery applications. The term“enhanced oil recovery” or “EOR” (also known as tertiary oil recovery),refers to a process for hydrocarbon production in which an aqueousinjection fluid comprising at least a water soluble polymer is injectedinto a hydrocarbon bearing formation.

In some embodiments, the one or more synthetic (co)polymers comprisewater-soluble synthetic (co)polymers. Examples of suitable synthetic(co)polymers include acrylic polymers, such as polyacrylic acids,polyacrylic acid esters, partly hydrolyzed acrylic esters, substitutedpolyacrylic acids such as polymethacrylic acid and polymethacrylic acidesters, polyacrylamides, partly hydrolyzed polyacrylamides, andpolyacrylamide derivatives such as acrylamide tertiary butyl sulfonicacid (ATBS); copolymers of unsaturated carboxylic acids, such as acrylicacid or methacrylic acid, with olefins such as ethylene, propylene andbutylene and their oxides; polymers of unsaturated dibasic acids andanhydrides such as maleic anhydride; vinyl polymers, such as polyvinylalcohol (PVA), N-vinylpyrrolidone, and polystyrene sulfonate; andcopolymers thereof, such as copolymers of these polymers with monomerssuch as ethylene, propylene, styrene, methylstyrene, and alkyleneoxides. In some embodiments, the one or more synthetic (co)polymer cancomprise polyacrylic acid (PAA), polyacrylamide (PAM), acrylamidetertiary butyl sulfonic acid (ATBS) (or AMPS,2-acrylamido-2-methylpropane sulfonic acid), N-vinylpyrrolidone (NVP),polyvinyl alcohol (PVA), or a blend or copolymer of any of thesepolymers. Copolymers may be made of any combination above, for example,a combination of NVP and ATBS. In certain examples, the one or moresynthetic (co)polymers can comprise acrylamide tertiary butyl sulfonicacid (ATBS) (or AMPS, 2-acrylamido-2-methylpropane sulfonic acid) or acopolymer thereof.

In some embodiments, the one or more synthetic (co)polymers can compriseacrylamide (co)polymers. In some embodiments, the one or more acrylamide(co)polymers comprise water-soluble acrylamide (co)polymers. In variousembodiments, the acrylamide (co)polymers comprise at least 30% byweight, or at least 50% by weight acrylamide units with respect to thetotal amount of all monomeric units in the (co)polymer.

Optionally, the acrylamide-(co)polymers can comprise, besidesacrylamide, at least one additional co-monomer. In example embodiments,the acrylamide-(co)polymer may comprise less than about 50%, or lessthan about 40%, or less than about 30%, or less than about 20% by weightof the at least one additional co-monomer. In some embodiments, theadditional comonomer can be a water-soluble, ethylenically unsaturated,in particular monoethylenically unsaturated, comonomer. Suitableadditional water-soluble comonomers include comonomers that are misciblewith water in any ratio, but it is sufficient that the monomers dissolvesufficiently in an aqueous phase to copolymerize with acrylamide. Insome cases, the solubility of such additional monomers in water at roomtemperature can be at least 50 g/L (e.g., at least 150 g/L, or at least250 g/L).

Other suitable water-soluble comonomers can comprise one or morehydrophilic groups. The hydrophilic groups can be, for example,functional groups that comprise one or more atoms selected from thegroup of O-, N-, S-, and P-atoms. Examples of such functional groupsinclude carbonyl groups >C—O, ether groups —O—, in particularpolyethylene oxide groups —(CH₂—CH₂—O—)_(n)—, where n is preferably anumber from 1 to 200, hydroxy groups —OH, ester groups —C(O)O—, primary,secondary or tertiary amino groups, ammonium groups, amide groups—C(O)—NH— or acid groups such as carboxyl groups —COOH, sulfonic acidgroups —SO₃H, phosphonic acid groups —PO₃H₂ or phosphoric acid groups—OP(OH)₃.

Examples of monoethylenically unsaturated comonomers comprising acidgroups include monomers comprising —COOH groups, such as acrylic acid ormethacrylic acid, crotonic acid, itaconic acid, maleic acid or fumaricacid, monomers comprising sulfonic acid groups, such as vinylsulfonicacid, allylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid,2-methacrylamido-2-methylpropanesulfonic acid,2-acrylamidobutanesulfonic acid, 3-acrylamido-3-methylbutanesulfonicacid or 2-acrylamido-2,4,4-trimethylpentanesulfonic acid, or monomerscomprising phosphonic acid groups, such as vinylphosphonic acid,allylphosphonic acid, N-(meth)acrylamidoalkylphosphonic acids or(meth)acryloyloxyalkyl-phosphonic acids. Of course the monomers may beused as salts.

The —COOH groups in polyacrylamide-copolymers may not only be obtainedby copolymerizing acrylic amide and monomers comprising —COOH groups butalso by hydrolyzing derivatives of —COOH groups after polymerization.For example, the amide groups —CO—NH₂ of acrylamide may hydrolyze thusyielding —COOH groups.

Also to be mentioned are derivatives of acrylamide thereof, such as, forexample, N-methyl(meth)acrylamide, N,N′-dimethyl(meth)acrylamide, andN-methylolacrylamide, N-vinyl derivatives such as N-vinylformamide,N-vinylacetamide, N-vinylpyrrolidone or N-vinylcaprolactam, and vinylesters, such as vinyl formate or vinyl acetate. N-vinyl derivatives canbe hydrolyzed after polymerization to vinylamine units, vinyl esters tovinyl alcohol units.

Other example comonomers include monomers comprising hydroxy and/orether groups, such as, for example, hydroxyethyl(meth)acrylate,hydroxypropyl(meth)acrylate, allyl alcohol, hydroxyvinyl ethyl ether,hydroxyl vinyl propyl ether, hydroxyvinyl butyl ether orpolyethyleneoxide(meth)acrylates.

Other example comonomers are monomers having ammonium groups, i.emonomers having cationic groups. Examples comprise salts of3-trimethylammonium propylacrylamides or 2-trimethylammoniumethyl(meth)acrylates, for example the corresponding chlorides, such as3-trimethylammonium propylacrylamide chloride (DIMAPAQUAT) and2-trimethylammonium ethyl methacrylate chloride (MADAME-QUAT).

Other example monoethylenically unsaturated monomers include monomerswhich may cause hydrophobic association of the (co)polymers. Suchmonomers comprise besides the ethylenic group and a hydrophilic partalso a hydrophobic part. Such monomers are disclosed for instance in WO2012/069477, which is incorporated herein by reference in its entirety.

Other example comonomers include N-alkyl acrylamides and N-alkylquarternary acrylamides, where the alkyl group comprises, for example, aC2-C28 alkyl group.

In certain embodiments, each of the one or more acrylamide-(co)polymerscan optionally comprise crosslinking monomers, i.e. monomers comprisingmore than one polymerizable group. In certain embodiments, the one ormore acrylamide-(co)polymers may optionally comprise crosslinkingmonomers in an amount of less than 0.5%, or 0.1%, by weight, based onthe amount of all monomers.

In an embodiment, each of the one or more acrylamide-(co)polymerscomprises at least one monoethylenically unsaturated comonomercomprising acid groups, for example monomers which comprise at least onegroup selected from —COOH, —SO₃H or —PO₃H₂. Examples of such monomersinclude but are not limited to acrylic acid, methacrylic acid,vinylsulfonic acid, allylsulfonic acid or2-acrylamido-2-methylpropanesulfonic acid, particularly preferablyacrylic acid and/or 2-acrylamido-2-methylpropanesulfonic acid and mostpreferred acrylic acid or the salts thereof. The amount of suchcomonomers comprising acid groups can be from 0.1% to 70%, from 1% to50%, or from 10% to 50% by weight based on the amount of all monomers.

In an embodiment, each of the one or more acrylamide-(co)polymerscomprise from 50% to 90% by weight of acrylamide units and from 10% to50% by weight of acrylic acid units and/or their respective salts, basedon the total weight of all the monomers making up the copolymer. In anembodiment, each of the one or more acrylamide-(co)polymers comprisefrom 60% to 80% by weight of acrylamide units and from 20% to 40% byweight of acrylic acid units, based on the total weight of all themonomers making up the copolymer.

In some embodiments, the one or more synthetic (co)polymers (e.g., theone or more acrylamide (co)polymers) are in the form of particles, whichare dispersed in the emulsion or LP. In some embodiments, the particlesof the one or more synthetic (co)polymers can have an average particlesize of from 0.4 μm to 5 μm, or from 0.5 μm to 2 μm. Average particlesize refers to the d₅₀ value of the particle size distribution (numberaverage) as measured by laser diffraction analysis.

In some embodiments, the one or more synthetic (co)polymers (e.g., theone or more acrylamide (co)polymers) can have a weight average molecularweight (M_(w)) of from 5,000,000 g/mol to 30,000,000 g/mol; from10,000,000 g/mol to 25,000,000 g/mol; or from 15,000,000 g/mol to25,000,000 g/mol.

In some embodiments, the LP composition can comprise one or moresynthetic (co)polymers (e.g., one or more acrylamide (co)polymers)dispersed in one or more hydrophobic liquids. In these embodiments, theamount of the one or more synthetic (co)polymers (e.g., one or moreacrylamide (co)polymers) in the LP composition can be at least 39% byweight, based on the total weight of the composition. In some of theseembodiments, the amount of the one or more synthetic (co)polymers (e.g.,one or more acrylamide-(co)polymers) in the LP composition can be from39% to 80% by weight, or from 40% to 60% by weight, or from 45% to 55%by weight, based on the total amount of all components of thecomposition (before dilution). In some embodiments, the amount of theone or more synthetic (co)polymers (e.g., one or moreacrylamide-(co)polymers) in the LP composition is 39%, 40%, 41%, 42%,43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%,57%, 58%, 59%, 60%, or higher, by weight, based on the total amount ofall components of the composition (before dilution).

In some embodiments, the LP composition can comprise one or moresynthetic (co)polymers (e.g., one or more acrylamide (co)polymers)emulsified in one or more hydrophobic liquids. In these embodiments, theamount of the one or more synthetic (co)polymers (e.g., one or moreacrylamide (co)polymers) in the LP composition can be less than 38% byweight, less than 35% by weight, or less than 30% by weight based on thetotal weight of the composition. In some of these embodiments, theamount of the one or more synthetic (co)polymers (e.g., one or moreacrylamide-(co)polymers) in the LP composition can be from 10% to 35% byweight, from 10% to 38% by weight, from 15% to 30% by weight, from 15%to 38% by weight, from 20% to 38% by weight, or from 20% to 30% byweight, based on the total amount of all components of the composition(before dilution). In some embodiments, the amount of the one or moresynthetic (co)polymers (e.g., one or more acrylamide-(co)polymers) inthe LP composition is 38%, 37%, 36%, 35%, 34%, 33%, 32%, 31%, 30%, 29%,28%, 27%, 26%, 25%, 24%, 23%, 22%, 21%, 20%, 19%, 18%, 17%, 16%, 15%,14%, 13%, 12%, 11%, or less, by weight, based on the total amount of allcomponents of the composition (before dilution).

Emulsifying Surfactants

In some embodiments, the LP composition can include one or moreemulsifying surfactants. In some embodiments, the one or moreemulsifying surfactants are surfactants capable of stabilizingwater-in-oil-emulsions. Emulsifying surfactants, among other things, inthe emulsion, lower the interfacial tension between the water and thewater-immiscible liquid so as to facilitate the formation of awater-in-oil polymer emulsion. It is known in the art to describe thecapability of surfactants to stabilize water-in-oil-emulsions oroil-in-water emulsions by using the so called “HLB-value”(hydrophilic-lipophilic balance). The HLB-value usually is a number from0 to 20. In surfactants having a low HLB-value the lipophilic parts ofthe molecule predominate and consequently they are usually goodwater-in-oil emulsifiers. In surfactants having a high HLB-value thehydrophilic parts of the molecule predominate and consequently they areusually good oil-in-water emulsifiers. In some embodiments, the one ormore emulsifying surfactants are surfactants having an HLB-value of from2 to 10, or a mixture of surfactant having an HLB-value of from 2 to 10.

Examples of suitable emulsifying surfactants include, but are notlimited to, sorbitan esters, in particular sorbitan monoesters withC12-C18-groups such as sorbitan monolaurate (HLB approx. 8.5), sorbitanmonopalmitate (HLB approx. 7.5), sorbitan monostearate (HLB approx.4.5), sorbitan monooleate (HLB approx. 4); sorbitan esters with morethan one ester group such as sorbitan tristearate (HLB approx. 2),sorbitan trioleate (HLB approx. 2); ethoxylated fatty alcohols with 1 to4 ethyleneoxy groups, e.g. polyoxyethylene (4) dodecylether ether (HLBvalue approx. 9), polyoxyethylene (2) hexadecyl ether (HLB value approx.5), and polyoxyethylene (2) oleyl ether (HLB value approx. 4).

Exemplary emulsifying surfactants include, but are not limited to,emulsifiers having HLB values of from 2 to 10 (e.g., less than 7).Suitable such emulsifiers include the sorbitan esters, phthalic esters,fatty acid glycerides, glycerine esters, as well as the ethoxylatedversions of the above and any other well known relatively low HLBemulsifier. Examples of such compounds include sorbitan monooleate, thereaction product of oleic acid with isopropanolamide, hexadecyl sodiumphthalate, decyl sodium phthalate, sorbitan stearate, ricinoleic acid,hydrogenated ricinoleic acid, glyceride monoester of lauric acid,glyceride monoester of stearic acid, glycerol diester of oleic acid,glycerol triester of 12-hydroxystearic acid, glycerol triester ofricinoleic acid, and the ethoxylated versions thereof containing 1 to 10moles of ethylene oxide per mole of the basic emulsifier. Thus, anyemulsifier can be utilized which will permit the formation of theinitial emulsion and stabilize the emulsion during the polymerizationreaction. Examples of emulsifying surfactants also include modifiedpolyester surfactants, anhydride substituted ethylene copolymers,N,N-dialkanol substituted fatty amides, and tallow amine ethoxylates.

In an embodiment, the inverse emulsion or LP composition comprises from0% to 5% by weight (e.g., from 0.05% to 5%, from 0.1% to 5%, or from0.5% to 3% by weight) of the one or more emulsifying surfactants, basedon the total weight of the composition. These emulsifying surfactantscan be used alone or in mixtures. In some embodiments, the inverseemulsion or LP composition can comprise less than 5% by weight (e.g.,less than 4% by weight, or less than 3% by weight) of the one or moreemulsifying surfactants, based on the total weight of the composition.

Process Stabilizing Agents

In some embodiments, the LP composition can optionally include one ormore process stabilizing agents. The process stabilizing agents aim atstabilizing the dispersion of the particles ofpolyacrylamide-(co)polymers in the organic, hydrophobic phase andoptionally also at stabilizing the droplets of the aqueous monomer phasein the organic hydrophobic liquid before and in course of thepolymerization or processing of the LP composition. The term“stabilizing” means in the usual manner that the agents prevent thedispersion from aggregation and flocculation.

The process stabilizing agents can be any stabilizing agents, includingsurfactants, which aim at such stabilization. In certain embodiments,the process stabilizing agents can be oligomeric or polymericsurfactants. Due to the fact that oligomeric and polymeric surfactantscan have many anchor groups they absorb very strongly on the surface ofthe particles and furthermore oligomers/polymers are capable of forminga dense steric barrier on the surface of the particles which preventsaggregation. The number average molecular weight Mn of such oligomericor polymeric surfactants may for example range from 500 to 60,000 g/mol(e.g., from 500 to 10,000 g/mol, or from 1,000 to 5,000 g/mol). Suitableoligomeric and/or polymeric surfactants for stabilizing polymerdispersions are known to the skilled artisan. Examples of suchstabilizing polymers comprise amphiphilic block copolymers, comprisinghydrophilic and hydrophobic blocks, amphiphilic copolymers comprisinghydrophobic and hydrophilic monomers and amphiphilic comb polymerscomprising a hydrophobic main chain and hydrophilic side chains oralternatively a hydrophilic main chain and hydrophobic side chains.

Examples of amphiphilic block copolymers comprise block copolymerscomprising a hydrophobic block comprising alkylacrylates having longeralkyl chains, e.g., C6 to C22-alkyl chains, such as for instancehexyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl(meth)acrylate,do-decyl(meth)acrylate, hexadecyl(meth)acrylate oroctadecyl(meth)acrylate. The hydrophilic block may comprise hydrophilicmonomers such as acrylic acid, methacrylic acid or vinyl pyrrolidone.

Inverting Surfactants

In some embodiments, the LP composition optionally can include one ormore inverting surfactants. In some embodiments, the one or moreemulsifying surfactants are surfactants which can be used to acceleratethe formation of an aqueous polymer solution (e.g., an inverted(co)polymer solution) after mixing the inverse emulsion or LPcomposition with an aqueous fluid.

Suitable inverting surfactants are known in the art, and include, forexample, nonionic surfactants comprising a hydrocarbon group and apolyalkylenoxy group of sufficient hydrophilic nature. In some cases,nonionic surfactants defined by the general formulaR¹—O—(CH(R²)—CH₂—O)_(n)H (I) can be used, wherein R¹ is aC₈-C₂₂-hydrocarbon group, such as an aliphatic C₁₀-C₁₈-hydrocarbongroup, n is a number of ≥4, preferably ≥6, and R² is H, methyl or ethyl,with the proviso that at least 50% of the groups R² are H. Examples ofsuch surfactants include polyethoxylates based on C₁₀-C₁₈-alcohols suchas C_(12/14)-, C_(14/18)- or C_(16/18)-fatty alcohols, C₁₃- orC_(13/15)-oxoalcohols. The HLB-value can be adjusted by selecting thenumber of ethoxy groups. Specific examples include tridecylalcoholethoxylates comprising from 4 to 14 ethylenoxy groups (e.g.,tridecyalcohol-8 EO (HLB-value approx. 13-14)) or C_(12/14) fattyalcohol ethoxylates (e.g., C_(12/14).8 EO (HLB-value approx. 13)).Examples of emulsifying surfactants also include modified polyestersurfactants, anhydride substituted ethylene copolymers, N,N-dialkanolsubstituted fatty amides, and tallow amine ethoxylates.

Other suitable inverting surfactants include anionic surfactants, suchas, for example, surfactants comprising phosphate or phosphonic acidgroups.

In some embodiments, the one or more inverting surfactants can comprisepolyoxyethylene sorbitol tetraoleate, C₁₂₋₁₄ branched ethoxylatedalcohol, polyethylene glycol monoleate. In certain embodiments, the oneor more inverting surfactants can comprise from 1 to 20 mole %polyoxyethylene sorbitol tetraoleate, from 60 to 80 mole % C₁₂₋₁₄branched ethoxylated alcohol and about 15 to about 25 mole %polyethylene glycol monoleate.

In some embodiments, the amount of the one or more inverting surfactantsin the inverse emulsion or LP composition is from 1% to 10% (e.g., from1% to 5%) by weight. based on the total amount of all components of theinverse emulsion or LP composition.

In certain embodiments, the one or more inverting surfactants can beadded to the inverse emulsion or LP composition directly afterpreparation of the composition comprising the one or more acrylamide(co)polymers dispersed in one or more hydrophobic liquids, andoptionally the one or more emulsifying surfactants (i.e., the inverseemulsion or liquid dispersion polymer composition which is transportedfrom the location of manufacture to the location of use alreadycomprises the one or more inverting surfactants). In another embodimentthe one or more inverting surfactants may be added to the inverseemulsion or LP composition at the location of use (e.g., at an off-shoreproduction site).

Other Components

Optional further components can be added to the inverse emulsion or LPcomposition. Examples of such components comprise radical scavengers,oxygen scavengers, chelating agents, biocides, stabilizers, orsacrificial agents.

Preparation of LP Compositions

In some embodiments, LP compositions can be synthesized as according tothe following procedures.

In a first step, an inverse emulsion (water-in-oil emulsion) ofacrylamide-(co)polymers can be synthesized using procedures known to theskilled artisan. Such inverse emulsions can be obtained by polymerizingan aqueous solution of acrylamide and other comonomers, such aswater-soluble ethylenically unsaturated comonomers, emulsified in ahydrophobic oil phase. In a following step, water within such inverseemulsions can be reduced to an amount of less than 10%, or less than 5%,by weight. Suitable techniques are described for instance in U.S. Pat.No. 4,052,353, U.S. Pat. No. 4,528,321, or DE 24 19 764 A1, each ofwhich is incorporated herein by reference in its entirety.

For the polymerization, an aqueous monomer solution comprisingacrylamide and optionally other comonomers can be prepared. Acrylamideis a solid at room temperature and aqueous solutions comprising around50% by weight of acrylamide are commercially available. If comonomerswith acidic groups such as acrylic acid are used the acidic groups maybe neutralized by adding aqueous bases such as aqueous sodium hydroxide.The concentration of all monomers together in the aqueous solutionshould usually be from 10% to 60% by weight based on the total of allcomponents of the monomer solution, or from 30% to 50%, or from 35% to45% by weight.

The aqueous solution of acrylamide and comonomers can be emulsified inthe one or more hydrophobic liquids using one or more emulsifyingsurfactants. The one or more emulsifying surfactants may be added to themixture or may be added to the monomer solution or the hydrophobicliquid before mixing. Other surfactants may be used in addition to theone or more emulsifying surfactants, such as a stabilizing surfactant.Emulsifying may be done in the usual manner, e.g. by stirring themixture.

After an emulsion has been formed polymerization may be initiated byadding oil- and/or water soluble initiators for radical polymerizationto the emulsion. The initiators may be dissolved in water or watermiscible organic solvents such as for instance alcohols. It may also beadded as emulsion. Exemplary polymerization initiators comprise organicperoxides such as tert-butyl hydroperoxide, sodium sulfite, sodiumdisulfite or organic sulfites, ammonium- or sodium peroxodisulfate,iron(II) salts or azo groups comprising initiators such as AIBN.

In certain embodiments, one or more chain transfer agents may be addedto the mixture during polymerization. Generally, chain transfer agentshave at least one weak chemical bond, which therefore facilitates thechain transfer reaction. Any conventional chain transfer agent may beemployed, such as propylene glycol, isopropanol, 2-mercaptoethanol,sodium hypophosphite, dodecyl mercaptan, thioglycolic acid, other thiolsand halocarbons, such as carbon tetrachloride. The chain transfer agentis generally present in an amount of from 0.001 percent to 10 percent byweight of the total emulsion, though more may be used.

The polymerization temperature usually is from 30° C. to 100° C., orfrom 30° C. to 70° C., or from 35° C. to 60° C. Heating may be done byexternal sources of heat and/or heat may be generated—in particular whenstarting polymerization—by the polymerization reaction itself.Polymerization times may for example be from about 0.5 h to about 10 h.

The polymerization yields an inverse emulsion comprising an aqueousphase of the one or more acrylamide-(co)polymers dissolved or swollen inwater wherein the aqueous phase is emulsified in an organic phasecomprising the one or more hydrophobic liquids.

In order to convert the inverse emulsion obtained to the LP compositionsto be used in the methods described herein, after the polymerization,some or all of the water is distilled off from the emulsion thusyielding particles of the one or more acrylamide-(co)polymers emulsifiedin the one or more hydrophobic liquids.

For the liquid polymer compositions, the water is at least removed to alevel of less than 10%, or less than 7%, or less than 5%, or less than3% by weight. In exemplary embodiments, the removal of water is carriedout by any suitable means, for example, at reduced pressure, e.g. at apressure of 30 hPa to 500 hPa, preferably 50 hPa to 250 hPa. Thetemperature in course of water removal may typically be from 70° C. to100° C., although techniques which remove water at higher temperaturesmay be used. In certain embodiments, one or more of the hydrophobicliquids used in the inverse emulsion may be a low boiling liquid, whichmay distill off together with the water as a mixture.

After removal of the amount of water desired, the one or more invertingsurfactants, and other optional components, can be added.

In some embodiments, the manufacture of the liquid polymer compositionsis carried out in a chemical production plant.

Preparation Aqueous Polymer Solutions

Provided herein are aqueous polymer solutions, as well as methods ofpreparing the aqueous polymer solutions from LP compositions, such asthose described above, using a single stage mixing process.

Methods for preparing an aqueous polymer solution from an LP compositioncomprising one or more synthetic (co)polymers (e.g., one or moreacrylamide (co)polymers) can comprise combining the LP composition withan aqueous fluid in a single stage mixing process to provide an aqueouspolymer solution having a concentration of one or more synthetic(co)polymers (e.g., one or more acrylamide (co)polymers) of from 50 to15,000 ppm.

In some embodiments, the aqueous polymer solution can have aconcentration of one or more synthetic (co)polymers (e.g., one or moreacrylamide (co)polymers) of at least 50 ppm (e.g., at least 100 ppm, atleast 250 ppm, at least 500 ppm, at least 750 ppm, at least 1000 ppm, atleast 1500 ppm, at least 2000 ppm, at least 2500 ppm, at least 3000 ppm,at least 3500 ppm, at least 4000 ppm, at least 4500 ppm, at least 5000ppm, at least 5500 ppm, at least 6000 ppm, at least 6500 ppm, at least7000 ppm, at least 7500 ppm, at least 8000 ppm, at least 8500 ppm, atleast 9000 ppm, at least 9500 ppm, at least 10,000 ppm, at least 10,500ppm, at least 11,000 ppm, at least 11,500 ppm, at least 12,000 ppm, atleast 12,500 ppm, at least 13,000 ppm, at least 13,500 ppm, at least14,000 ppm, or at least 14,500 ppm).

In some embodiments, the aqueous polymer solution can have aconcentration of one or more synthetic (co)polymers (e.g., one or moreacrylamide (co)polymers) of 15,000 ppm or less (e.g., 14,500 ppm orless, 14,000 ppm or less, 13,500 ppm or less, 13,000 ppm or less, 12,500ppm or less, 12,000 ppm or less, 11,500 ppm or less, 11,000 ppm or less,10,500 ppm or less, 10,000 ppm or less, 9,500 ppm or less, 9,000 ppm orless, 8,500 ppm or less, 8,000 ppm or less, 7,500 ppm or less, 7,000 ppmor less, 6,500 ppm or less, 6,000 ppm or less, 5,500 ppm or less, 5,000ppm or less, 4500 ppm or less, 4000 ppm or less, 3500 ppm or less, 3000ppm or less, 2500 ppm or less, 2000 ppm or less, 1500 ppm or less, 1000ppm or less, 750 ppm or less, 500 ppm or less, 250 ppm or less, or 100ppm or less).

The aqueous polymer solution can have a concentration of one or moresynthetic (co)polymers (e.g., one or more acrylamide (co)polymers)ranging from any of the minimum values described above to any of themaximum values described above. For example, in some embodiments, theaqueous polymer solution can have a concentration of one or moresynthetic (co)polymers (e.g., one or more acrylamide (co)polymers) offrom 500 to 5000 ppm (e.g., from 500 to 3000 ppm, or from 500 to 1500ppm).

In some embodiments, the aqueous polymer solution can be an aqueousunstable colloidal suspension. In other embodiments, the aqueous polymersolution can be an aqueous stable solution.

In some embodiments, the aqueous polymer solution can have a filterratio of 1.5 or less (e.g., 1.45 or less, 1.4 or less, 1.35 or less, 1.3or less, 1.25 or less, 1.2 or less, 1.15 or less, 1.1 or less, or lessthan 1.05) at 15 psi using a 1.2 μm filter. In some embodiments, theaqueous polymer solution can have a filter ratio of greater than 1(e.g., at least 1.05, at least 1.1, at least 1.15, at least 1.2, atleast 1.25, at least 1.3, at least 1.35, at least 1.4, or at least 1.45)at 15 psi using a 1.2 μm filter.

The aqueous polymer solution can a filter ratio at 15 psi using a 1.2 μmfilter ranging from any of the minimum values described above to any ofthe maximum values described above. For example, in some embodiments,the aqueous polymer solution can have a filter ratio of from 1 to 1.5(e.g., from 1.1 to 1.4, or from 1.1 to 1.3) at 15 psi using a 1.2 μmfilter.

In certain embodiments, the aqueous polymer solution can have aviscosity based on shear rate, temperature, salinity, polymerconcentration, and polymer molecular weight. In some embodiments, theaqueous polymer solution can have a viscosity of from 2 cP to 100 cP,where the 2 cP to 100 cP is an output using the ranges in the followingtable:

Polymer viscosity (cP) 2~100 Shear rate (1/sec) 0.1~1000  Temperature (°C.) 1~120 Salinity (ppm)    0~250,000 Polymer concentration (ppm)  50~15,000 Polymer molecular weight (Dalton) 2M~26M 

In some embodiments, the aqueous polymer solution can have a viscosityof from 25 cP to 35 cP at 30° C. In some embodiments, the aqueouspolymer solution can have a viscosity of greater than 10 cP at 40° C. Incertain embodiments, the aqueous polymer solution can have a viscosityof from 20 cP to 30 cP at 40° C.

In some embodiments, when the LP composition is combined with an aqueousfluid, providing an aqueous polymer solution having from 50 to 15,000ppm, from 500 to 5,000 ppm, or from 500 to 3000 ppm, active polymer, theaqueous polymer solution has a viscosity of at least 20 cP at 40° C.,and a filter ratio (FR) (1.2 micron filter) of 1.5 or less. In certainembodiments, when the LP composition is combined with in an aqueousfluid, providing an aqueous polymer solution having from 50 to 15,000ppm, from 500 to 5000 ppm, or from 500 to 3000 ppm, active polymer, theaqueous polymer solution has a viscosity of at least 20 cP at 30° C.,and a filter ratio (FR) (1.2 micron filter) of 1.5 or less.

In some cases, combining an LP composition with an aqueous fluid cancomprise inverting the LP composition in an aqueous fluid to provide theaqueous polymer solution. In these embodiments, the aqueous polymersolution can be said to be an “inverted polymer solution.” As usedherein, “inverted” refers to the point at which the viscosity of theaqueous polymer solution has substantially reached a consistentviscosity. In practice, this may be determined for example by measuringviscosity of the aqueous polymer solution periodically over time andwhen three consecutive measurements are within the standard of error forthe measurement, then the composition is considered inverted. In someembodiments, inversion of the LP forms an inverted polymer solution in30 minutes or less (e.g., 15 minutes or less, 10 minutes or less, 5minutes or less, or less).

As described above, methods for preparing an aqueous polymer solutionfrom an LP composition comprising one or more synthetic (co)polymers(e.g., one or more acrylamide (co)polymers) can comprise combining theLP composition with an aqueous fluid in a single stage mixing process toprovide an aqueous polymer solution having a concentration of one ormore synthetic (co)polymers (e.g., one or more acrylamide (co)polymers)of from 50 to 15,000 ppm. The single stage mixing process can compriseapplying a specific mixing energy of at least 0.10 kJ/kg to the LPcomposition and the aqueous fluid.

In some embodiments, the single stage mixing process can compriseapplying a specific mixing energy of at least 0.10 kJ/kg (e.g., at least0.15 kJ/kg, at least 0.20 kJ/kg, at least 0.25 kJ/kg, at least 0.30kJ/kg, at least 0.35 kJ/kg, at least 0.40 kJ/kg, at least 0.45 kJ/kg, atleast 0.50 kJ/kg, at least 0.55 kJ/kg, at least 0.60 kJ/kg, at least0.65 kJ/kg, at least 0.70 kJ/kg, at least 0.75 kJ/kg, at least 0.80kJ/kg, at least 0.85 kJ/kg, at least 0.90 kJ/kg, at least 0.95 kJ/kg, atleast 1.00 kJ/kg, at least 1.05 kJ/kg, at least 1.10 kJ/kg, at least1.15 kJ/kg, at least 1.20 kJ/kg, at least 1.25 kJ/kg, at least 1.30kJ/kg, at least 1.35 kJ/kg, at least 1.40 kJ/kg, or at least 1.45 kJ/kg)to the LP composition and the aqueous fluid. In some embodiments, thesingle stage mixing process can comprise applying a specific mixingenergy of 1.50 kJ/kg or less (e.g., 1.45 kJ/kg or less, 1.40 kJ/kg orless, 1.35 kJ/kg or less, 1.30 kJ/kg or less, 1.25 kJ/kg or less, 1.20kJ/kg or less, 1.15 kJ/kg or less, 1.10 kJ/kg or less, 1.05 kJ/kg orless, 1.00 kJ/kg or less, 0.95 kJ/kg or less, 0.90 kJ/kg or less, 0.85kJ/kg or less, 0.80 kJ/kg or less, 0.75 kJ/kg or less, 0.70 kJ/kg orless, 0.65 kJ/kg or less, 0.60 kJ/kg or less, 0.55 kJ/kg or less, 0.50kJ/kg or less, 0.45 kJ/kg or less, 0.40 kJ/kg or less, 0.35 kJ/kg orless, 0.30 kJ/kg or less, 0.25 kJ/kg or less, 0.20 kJ/kg or less, or0.15 kJ/kg or less) to the LP composition and the aqueous fluid.

The single stage mixing process can comprise applying a specific mixingenergy to the LP composition and the aqueous fluid ranging from any ofthe minimum values described above to any of the maximum valuesdescribed above. For example, in some embodiments, the single stagemixing process can comprise applying a specific mixing energy of from0.10 kJ/kg to 1.50 kJ/kg (e.g., from 0.15 kJ/kg to 1.40 kJ/kg, from 0.15kJ/kg to 1.20 kJ/kg) to the LP composition and the aqueous fluid.

The LP composition can be combined with an aqueous fluid in a batchprocess or a continuous process. In certain embodiments, the The LPcomposition is combined with an aqueous fluid in a continuous process.For example, the LP composition can be combined with an aqueous fluid asa continuous process to produce a fluid stream for injection into ahydrocarbon-bearing formation. A continuous process is a process thatcan be effected without the need to be intermittently stopped or slowed.For example, continuous processes can meet one or more of the followingcriteria: (a) materials for forming the aqueous polymer solution (e.g.,the LP composition and the aqueous fluid) are fed into the system inwhich the aqueous polymer solution is produced at the same rate as theaqueous polymer solution is removed from the system; (b) the nature ofthe composition(s) introduced to the system in which the aqueous polymersolution is produced is a function of the composition(s) position withthe process as it flows from the point at which the composition(s) areintroduced to the system to the point at which the aqueous polymersolution is removed from the system; and/or (c) the quantity of aqueouspolymer solution produced is a function of (i) the duration for whichthe process is operated and (ii) the throughput rate of the process.

As discussed above, methods for preparing an aqueous polymer solutionfrom an LP composition can comprise combining the LP composition with anaqueous fluid in a single stage mixing process. As used herein, thephase “single stage mixing process” refers to mixing processes where anLP composition and an aqueous fluid are combined in their finalproportions either before mixing or within a first mixer, such that thefluid exiting the first mixer includes all components of the finalaqueous polymer solution at their final concentration. Optionally, thefluid exiting the first mixer can undergo additional mixing steps;however, additional volumes of the LP composition or the aqueous fluidare not added once the fluid exits the first mixer. In this context,single stage mixing processes can be distinguished from conventionaldual-stage and multistage mixing processes commonly used to prepareaqueous polymer solutions. Dual-stage and multistage mixing processesgenerally involve the combination of an LP composition and an aqueousfluid either before mixing or within a first mixer to produce aconcentrated composition, which must then be diluted with additionalaqueous fluid after leaving the first mixer to produce a fluid thatincludes all of the components of the final aqueous polymer solution attheir final concentrations.

The single stage mixing process can comprise a single mixing step, or aplurality of mixing steps (i.e., two or more steps). In single stagemixing processes that comprise a single mixing step, an LP compositionand an aqueous fluid are combined in their final proportions (eitherbefore mixing or within a first mixer), mixed within a first mixer, andexit the first mixer as an aqueous polymer solution. For example, apolymer feed stream comprising the LP composition can be combined (e.g.,in a fixed ratio) with an aqueous fluid stream upstream of or within anin-line mixer. The combined fluid stream can then pass through thein-line mixer, emerging as the aqueous polymer solution. In someembodiments, the in-line mixer can have a mixer inlet and a mixeroutlet, and the difference in pressure between the mixer inlet and themixer outlet can be from 15 psi to 400 psi (e.g., from 15 psi to 150psi, from 15 psi to 100 psi, or from 15 psi to 75 psi).

An example system for the preparation of an aqueous polymer solution ina single mixing step is illustrated schematically in FIG. 1. As shown inFIG. 1, a pump 102 can be used to inject a stream of the LP composition104 into a line 106 carrying the aqueous fluid stream. The combinedfluid stream can then pass through an in-line mixer 108 having a mixerinlet 110 and a mixer outlet 112, emerging as the aqueous polymersolution. The pressure drop through the in-line mixer 108 (Δp) can befrom 15 psi to 400 psi (e.g., from 15 psi to 150 psi, from 15 psi to 100psi, or from 15 psi to 75 psi).

In other embodiments, the single stage mixing process comprise two ormore mixing steps (e.g., a first mixing step in which an LP compositionand an aqueous fluid are combined in their final proportions (eitherbefore mixing or within a first mixer), mixed within a first mixer, andexit the first mixer as a partially mixed aqueous polymer solution; andone or more additional mixing steps in which the partially mixed aqueouspolymer solution is mixed within one or more additional mixers toproduce the final aqueous polymer solution). For example, the singlestage mixing process can comprise two, three, four, five, or moreconsecutive mixing steps. In certain cases, the single stage mixingprocess can comprise two mixing steps.

An example system for the preparation of an aqueous polymer solution intwo mixing steps is illustrated schematically in FIG. 2. As shown inFIG. 2, pumps 102 can be used to inject a stream of the LP composition104 and a stream of aqueous fluid 106 through a first in-line mixer 108having a first mixer inlet 110 and a first mixer outlet 112, emerging asa stream of partially mixed aqueous polymer solution 114. The partiallymixed aqueous polymer solution can comprise a concentration of synthetic(co)copolymer of from 50 to 15,000 ppm (e.g., from 500 to 5000 ppm, orfrom 500 to 3000 ppm). The pressure drop through the first in-line mixer108 (Δp1) can be from 15 psi to 400 psi (e.g., from 15 psi to 150 psi,from 15 psi to 100 psi, or from 15 psi to 75 psi). The stream ofpartially mixed aqueous polymer solution 114 can then pass through asecond in-line mixer 116 having a second mixer inlet 118 and a secondmixer outlet 120, emerging as a stream of aqueous polymer solution 122.The pressure drop through the second in-line mixer 116 (Δp2) can be from15 psi to 400 psi (e.g., from 15 psi to 150 psi, from 15 psi to 100 psi,or from 15 psi to 75 psi). In some embodiments, the first in-line mixercan comprise a static mixer and the second in-line mixer can comprise astatic mixer. In other examples, the first in-line mixer can comprise astatic mixer and the second in-line mixer can comprise a dynamic mixer.

In some embodiments, the single stage mixing process for preparing anaqueous polymer solution can comprise parallel single mixing steps,parallel multiple mixing steps, or a combination thereof. An examplesystem for the preparation of an aqueous polymer solutions usingparallel mixing steps (e.g., parallel single mixing steps, parallelmultiple mixing steps, or a combination thereof) is illustratedschematically in FIG. 3. As shown in FIG. 3, a pump 102 can be used todirect a stream of the LP composition 104 to LP manifold 122. LPmanifold 122 can include an LP manifold inlet 124 through which the LPcomposition enters the LP manifold 122, and a plurality of LP manifoldoutlets 126 (in this example three manifold outlets) through whichstreams of the LP composition exit the LP manifold 122. The system canalso include a main line 103 carrying an aqueous fluid stream to aqueousfluid manifold 128. The aqueous fluid manifold 128 can include anaqueous fluid manifold inlet 130 through which the aqueous fluid entersthe aqueous fluid manifold 128, and a plurality of aqueous fluidmanifold outlets 132 (in this example three manifold outlets) throughwhich streams of the aqueous fluid exit the aqueous fluid manifold 128.Each stream of LP composition exiting LP manifold 122 can then becombined with a stream of aqueous fluid exiting the aqueous fluidmanifold 128 in a different configuration of in-line mixers 134, therebyforming a plurality of streams of the aqueous polymer solution inparallel. Each configuration of in-line mixers 134 can include,independently, a single in-line mixer or a plurality of in-line mixersfluidly connected in series (e.g., as shown in FIGS. 1 and 2). Byselecting appropriate configurations of in-line mixers 134, system forthe preparation of an aqueous polymer solutions that employ parallelsingle steps, parallel multiple steps, or any combination thereof can bereadily fabricated.

In some embodiments, the single stage mixing process can compriseparallel single mixing steps, parallel multiple mixing steps, or acombination thereof that are carried out in a polymer mixing system. Incertain examples, the mixing system can be positioned subsea. Examplepolymer mixing systems that can be used to conduct a single stage mixingprocess comprising parallel single mixing steps are schematicallyillustrated in FIGS. 4A and 4B. As shown in FIG. 4A, the system caninclude a main polymer feed line 202 diverging to a plurality of polymersupply branches 204, a main aqueous feed line 206 diverging to aplurality of aqueous supply branches 208, and a plurality of mixerarrangements 210 (only one of which is illustrated in FIG. 4A forclarity). In other examples, as shown in FIG. 4B, the main polymer feedline 202 can be fluidly connected to the plurality of polymer supplybranches 204 via a polymer distribution manifold 224. The polymerdistribution manifold 224 can be configured to independently control thefluid flow rate through each of the plurality of polymer supply branches204.

Referring again to FIG. 4A, each of the plurality of mixer arrangements210 is supplied by one of the plurality of polymer supply branches 204and one of the plurality of aqueous supply branches 208. Each of theplurality of mixer arrangements 210 can comprise an in-line mixer 212having a mixer inlet 214 and a mixer outlet 216.

Optionally, the mixing system can further comprise a flow control valve220 operably coupled to each the plurality of polymer supply branches204 to control fluid flow rate through each of the plurality of polymersupply branches. Optionally, the mixing system can further comprise aflow control valve 222 operably coupled to each the plurality of aqueoussupply branches 208 to control fluid flow rate through each of theplurality of aqueous supply branches. In certain embodiments, the mixingsystem can further comprise a flow control valve 220 operably coupled toeach the plurality of polymer supply branches 204 to control fluid flowrate through each of the plurality of polymer supply branches, and aflow control valve 222 operably coupled to each the plurality of aqueoussupply branches 208 to control fluid flow rate through each of theplurality of aqueous supply branches. Examples of suitable flow controlvalves include, for example, choke valves, chemical injection meteringvalves (CIMVs), and control valves.

Referring still to FIG. 4A, the LP composition and the aqueous fluid canbe combined in the polymer mixing system by passing the LP polymercomposition through the main polymer feed line 202 and the plurality ofpolymer supply branches 204 to reach each of the plurality of mixerarrangements 210. The LP polymer composition and the aqueous fluid canthen flow through the in-line mixer 212 of each of the plurality ofmixer arrangements 210 to provide a stream of the aqueous polymersolution 218. The pressure drop through the in-line mixer 212 (Δp) canbe from 15 psi to 400 psi (e.g., from 15 psi to 150 psi, from 15 psi to100 psi, or from 15 psi to 75 psi). In some embodiments, the LP polymercomposition and the aqueous fluid can flow through the in-line mixer 212of each of the plurality of mixer arrangements 210 at a velocity of from1 m/s to 4 m/s.

Example polymer mixing systems that can be used to conduct a singlestage mixing process comprising parallel multiple mixing steps areschematically illustrated in FIGS. 5A and 5B. As shown in FIG. 5A, thesystem can include a main polymer feed line 302 diverging to a pluralityof polymer supply branches 304, a main aqueous feed line 306 divergingto a plurality of aqueous supply branches 308, and a plurality of mixerarrangements 310 (only one of which is illustrated in FIG. 5A forclarity). In other examples, as shown in FIG. 5B, the main polymer feedline 302 can be fluidly connected to the plurality of polymer supplybranches 304 via a polymer distribution manifold 332. The polymerdistribution manifold 332 can be configured to independently control thefluid flow rate through each of the plurality of polymer supply branches304.

Referring again to FIG. 5A, each of the plurality of mixer arrangements310 is supplied by one of the plurality of polymer supply branches 304and one of the plurality of aqueous supply branches 308. Each of theplurality of mixer arrangements 310 can comprise a first in-line mixer312 having a first mixer inlet 314 and a first mixer outlet 316 inseries with a second in-line mixer 318 having a second mixer inlet 320and a second mixer outlet 322.

Optionally, the mixing system can further comprise a flow control valve324 operably coupled to each the plurality of polymer supply branches304 to control fluid flow rate through each of the plurality of polymersupply branches. Optionally, the mixing system can further comprise aflow control valve 326 operably coupled to each the plurality of aqueoussupply branches 308 to control fluid flow rate through each of theplurality of aqueous supply branches. In certain embodiments, the mixingsystem can further comprise a flow control valve 324 operably coupled toeach the plurality of polymer supply branches 304 to control fluid flowrate through each of the plurality of polymer supply branches, and aflow control valve 326 operably coupled to each the plurality of aqueoussupply branches 308 to control fluid flow rate through each of theplurality of aqueous supply branches. Examples of suitable flow controlvalves include, for example, choke valves, chemical injection meteringvalves (CIMVs), and control valves.

Referring still to FIG. 5A, the LP composition and the aqueous fluid canbe combined in the polymer mixing system by passing the LP polymercomposition through the main polymer feed line 302 and the plurality ofpolymer supply branches 304 to reach each of the plurality of mixerarrangements 310. The LP polymer composition and the aqueous fluid canthen flow through the through a first in-line mixer 312 having a firstmixer inlet 314 and a first mixer outlet 316, emerging as a stream ofpartially mixed aqueous polymer solution 328. The partially mixedaqueous polymer solution can comprise a concentration of synthetic(co)copolymer of from 50 to 15,000 ppm (e.g., from 500 to 5000 ppm, orfrom 500 to 3000 ppm). The pressure drop through the first in-line mixer312 (Δp1) can be from 15 psi to 400 psi (e.g., from 15 psi to 150 psi,from 15 psi to 100 psi, or from 15 psi to 75 psi). In some embodiments,the LP polymer composition and the aqueous fluid can flow through thefirst in-line mixer 312 of each of the plurality of mixer arrangements310 at a velocity of from 1 m/s to 4 m/s. The stream of partially mixedaqueous polymer solution 328 can then pass through a second in-linemixer 318 having a second mixer inlet 320 and a second mixer outlet 322,emerging as a stream of aqueous polymer solution 330. The pressure dropthrough the second in-line mixer 318 (Δp2) can be from 15 psi to 400 psi(e.g., from 15 psi to 150 psi, from 15 psi to 100 psi, or from 15 psi to75 psi). In some embodiments, the partially mixed aqueous polymersolution 328 can flow through the second in-line mixer 318 of each ofthe plurality of mixer arrangements 310 at a velocity of from 1 m/s to 4m/s. In some embodiments, the first in-line mixer can comprise a staticmixer and the second in-line mixer can comprise a static mixer. In otherexamples, the first in-line mixer can comprise a static mixer and thesecond in-line mixer can comprise a dynamic mixer.

Any suitable in-line mixer(s) can be used in conjunction with themethods and systems described above. Each in-line mixer can be a dynamicmixer or a static mixer. Suitable dynamic mixers, which involvemechanical agitation of one type or another, are known in the art, andinclude impeller mixers, turbine mixers, rotor-stator mixers, colloidmills, pumps, and pressure homogenizers. In certain embodiment, thein-line mixer(s) can comprise a dynamic mixer such as an electricalsubmersible pump, hydraulic submersible pump, or a progressive cavitypump. In certain embodiments, the in-line mixer(s) can comprise staticmixers. Static mixers are mixers that mix fluids in flow without the useof moving parts. Static mixers are generally constructed from a seriesof stationary, rigid elements that form intersecting channels to split,rearrange and combine component streams resulting in one homogeneousfluid stream. Static mixers provide simple and efficient solutions tomixing and contacting problems. More affordable than dynamic agitatorsystems, static mixing units have a long life with minimal maintenanceand low pressure drop. Static mixers can be fabricated from metalsand/or plastics to fit pipes and vessels of virtually any size andshape. In some cases, the static mixer can comprise a region of pipe,for example a serpentine region of pipe that facilitates mixing.

The aqueous fluid combined with the LP composition can comprise from 0to 250,000 ppm; 15,000 to 160,000 ppm; from 15,000 to 100,000 ppm; from10,000 to 50,000 ppm; from 15,000 to 50,000 ppm; from 30,000 to 40,000ppm; from 10,000 to 25,000 ppm; from 10,000 to 20,000 ppm; or from15,000 to 16,000 ppm total dissolved solids (tds). In an exampleembodiment, the aqueous fluid can comprise a brine having about 15,000ppm tds. In one embodiment, the brine may be a synthetic seawater brineas illustrated in the table below.

Composition of an Example Synthetic Seawater Brine Ions (ppm) SyntheticSeawater Brine Na+ 10800 K+ 400 Ca++ 410 Mg++ 1280 Cl− 19400 TDS 32290

The aqueous fluid combined with the LP compositions can compriseproduced reservoir brine, reservoir brine, sea water, fresh water,produced water, water, saltwater (e.g. water containing one or moresalts dissolved therein), brine, synthetic brine, synthetic seawaterbrine, or any combination thereof. Generally, the aqueous fluid cancomprise water from any readily available source, provided that it doesnot contain an excess of compounds that may adversely affect othercomponents in the aqueous polymer solution or render the aqueous polymersolution unsuitable for its intended use (e.g., unsuitable for use in anoil and gas operation such as an EOR operation). If desired, aqueousfluids obtained from naturally occurring sources can be treated prior touse. For example, aqueous fluids can be softened (e.g., to reduce theconcentration of divalent and trivalent ions in the aqueous fluid) orotherwise treated to adjust their salinity. In certain embodiments, theaqueous fluid can comprise soft brine or hard brine. In certainembodiments, the aqueous fluid can comprise produced reservoir brine,reservoir brine, sea water, or a combination thereof.

In one embodiment, seawater is used as the aqueous fluid, sinceoff-shore production facilities tend to have an abundance of seawateravailable, limited storage space, and transportation costs to and froman off-shore site are typically high. If seawater is used as the aqueousfluid, it can be softened prior to the addition of the suspendedpolymer, thereby removing multivalent ions in the water (e.g.,specifically Mg²⁺ and Ca²⁺).

In some embodiments, the aqueous fluid can have a temperature of from 1°C. to 120° C. In other embodiments, the aqueous fluid can have atemperature of from 45° C. to 95° C.

The methods described herein can be specifically adapted for use in aparticular oil and gas operation. For example, in some embodiments, theprocesses for preparing aqueous polymer solutions described herein canbe performed as a continuous process to produce a fluid stream forinjection into a hydrocarbon-bearing formation.

In some cases, the in-line mixer (or one or more in-line mixers in thecase of methods that include multiple mixing steps, parallel singlemixing steps, or parallel multiple mixing steps) can be arrangeddownstream from pumping equipment at the surface (e.g., on land, on avessel, or on an offshore platform) that pumps the LP composition andthe aqueous fluid. In certain embodiments, the in-line mixer (or one ormore in-line mixers in the case of methods that include multiple mixingsteps, parallel single mixing steps, or parallel multiple mixing steps)can be positioned at or near the wellhead of a well. In certainembodiments, the in-line mixer can be arranged downhole. In certainembodiments, the in-line mixer (or one or more in-line mixers in thecase of methods that include multiple mixing steps, parallel singlemixing steps, or parallel multiple mixing steps) can be positionedsubsurface, subsea, or downhole.

In certain embodiments, the hydrocarbon-bearing formation can be asubsea reservoir. In these embodiments, the in-line mixer (or one ormore in-line mixers in the case of methods that include multiple mixingsteps, parallel single mixing steps, or parallel multiple mixing steps)can be arranged downstream from pumping equipment at the surface (e.g.,on shore, on a vessel, or on an offshore platform) that pumps the LPcomposition and/or the aqueous fluid. In certain embodiments, thein-line mixer (or one or more in-line mixers in the case of methods thatinclude multiple mixing steps, parallel single mixing steps, or parallelmultiple mixing steps) can be positioned subsea. Thus, depending on theoil and gas operation, for example, an in-line mixer can be positionedon the surface, subsurface, subsea, or downhole.

As discussed above, the aqueous polymer solutions described herein canbe used oil and gas operations, such as EOR operations. For example, theaqueous polymer solutions described above can be used in polymerflooding operations. In some cases, the aqueous polymer solution furtherincludes one or more additional agents to facilitate hydrocarbonrecovery. For example, the aqueous polymer solution can further includea surfactant, an alkalinity agent, a co-solvent, a chelating agent, orany combination thereof. As such, the aqueous polymer solution can beused in polymer (P), alkaline-polymer (AP), surfactant-polymer (SP),and/or in alkaline-surfactant-polymer (ASP)-type EOR operations. Whenpresent, these additional components can be incorporated into theaqueous fluid prior to combination with the LP composition, such thatthe resulting aqueous polymer solution formed by combination of theaqueous fluid and the LP composition includes one or more of theseadditional components. Likewise, these additional components can also beincorporated to the LP composition prior to combination with the aqueousfluid, such that the resulting aqueous polymer solution formed bycombination of the aqueous fluid and the LP composition includes one ormore of these additional components. Alternatively, these additionalcomponents can be incorporated to the aqueous polymer solutionsfollowing combination with the LP composition.

For chemical enhanced oil recovery (CEOR) operations, the LP compositioncan be combined with an effective amount of aqueous fluid to provide anaqueous polymer solution (e.g., which can serve as an injection stream)with a target hydrated polymer concentration and particle size. Thetarget concentration varies according to the type of polymer employed,as well as the characteristics of the reservoir, e.g., petrophysicalrock properties, reservoir fluid properties, reservoir conditions suchas temperature, permeability, water compositions, mineralogy and/orreservoir location, etc. In some cases, the aqueous polymer solutionsdescribed herein are suitable for use in reservoirs with a permeabilityof from 10 millidarcy to 40,000 millidarcy.

The hydrated polymer molecules in the aqueous polymer solution can havea particle size (radius of gyration) ranging from 0.01 to 10 μm in oneembodiment. One reservoir characteristic is the median pore throats,which correspond to the permeability of the reservoirs. Depending on thereservoir, the median pore throats in reservoirs may range from 0.01 μmto several hundred micrometers. Since the size of hydrated polymers inwater range from 0.01 micrometer to several micrometers depending on thespecies, molecules, and reservoir conditions, in one embodiment,appropriate polymers are selected for LP composition to afford anaqueous polymer solution where the particle size of the hydrated polymeris <10% of the median pore throat parameters. This can allow thehydrated polymer particles to flow through the porous medium in anuninhibited manner. In another embodiment, the hydrated polymerparticles have an average particle size ranging from 2 to 8% of themedian pore throat size.

Surfactants can be included to lower the interfacial tension between theoil and water phase to less than about 10-2 dyne/cm (for example) andthereby recover additional oil by mobilizing and solubilizing oiltrapped by capillary forces. Examples of surfactants that can beutilized include, but are not limited to, anionic surfactants, cationicsurfactants, amphoteric surfactants, non-ionic surfactants, or acombination thereof. Anionic surfactants can include sulfates,sulfonates, phosphates, or carboxylates. Such anionic surfactants areknown and described in the art in, for example, U.S. Pat. No. 7,770,641,incorporated herein by reference in its entirety. Examples of specificanionic surfactants include internal olefin sulfonates, isomerizedolefin sulfonates, alkyl aryl sulfonates, medium alcohol (C10 to C17)alkoxy sulfates, alcohol ether [alkoxy] carboxylates, and alcohol ether[alkoxy] sulfates. Example cationic surfactants include primary,secondary, or tertiary amines, or quaternary ammonium cations. Exampleamphoteric surfactants include cationic surfactants that are linked to aterminal sulfonate or carboxylate group. Example non-ionic surfactantsinclude alcohol alkoxylates such as alkylaryl alkoxy alcohols or alkylalkoxy alcohols. Other non-ionic surfactants can include alkylalkoxylated esters and alkyl polyglycosides. In some embodiments,multiple non-ionic surfactants such as non-ionic alcohols or non-ionicesters are combined. As a skilled artisan may appreciate, thesurfactant(s) selection may vary depending upon such factors assalinity, temperature, and clay content in the reservoir.

Suitable alkalinity agents include basic, ionic salts of alkali metalsor alkaline earth metals. Alkalinity agents can be capable of reactingwith an unrefined petroleum acid (e.g. the acid or its precursor incrude oil (reactive oil)) to form soap (a surfactant which is a salt ofa fatty acid) in situ. These in situ generated soaps can serve as asource of surfactants causing a reduction of the interfacial tension ofthe oil in water emulsion, thereby reducing the viscosity of theemulsion. Examples of alkali agents include alkali metal hydroxides,carbonates, or bicarbonates, including, but not limited to, sodiumcarbonate, sodium bicarbonate, sodium hydroxide, potassium hydroxide,sodium silicate, tetrasodium EDTA, sodium metaborate, sodium citrate,and sodium tetraborate. In some cases, the alkalinity agent can bepresent in the inverted polymer solution in an amount of from 0.3 to 5.0weight percent of the solution, such as 0.5 to 3 weight percent.

The aqueous polymer solution can optionally include a co-solvent. A“co-solvent” refers to a compound having the ability to increase thesolubility of a solute in the presence of an unrefined petroleum acid.In embodiments, the co-solvents provided herein have a hydrophobicportion (alkyl or aryl chain), a hydrophilic portion (e.g. an alcohol)and optionally an alkoxy portion. Co-solvents as provided herein includealcohols (e.g. C₁-C₆ alcohols, C₁-C₆ diols), alkoxy alcohols (e.g. C₁-C₆alkoxy alcohols, C₁-C₆ alkoxy diols, and phenyl alkoxy alcohols), glycolether, glycol and glycerol. The term “alcohol” is used according to itsordinary meaning and refers to an organic compound containing an —OHgroups attached to a carbon atom. The term “diol” is used according toits ordinary meaning and refers to an organic compound containing two—OH groups attached to two different carbon atoms. The term “alkoxyalcohol” is used according to its ordinary meaning and refers to anorganic compound containing an alkoxy linker attached to a —OH group.

The aqueous polymer solution can optionally include a chelant orchelating agent. Chelants may be used to complex with the alkali metaland soften brines. If desired, the salinity of the aqueous polymersolution may be optimized for a particular subterranean reservoir byadjusting a number of chelating ligands in the chelating agent, such asalkoxylate groups if the chelant is EDTA (“ethylenediaminetetraaceticacid”). EDTA is just one example of a suitable chelant, another exampleof a chelant is MGDA (“methylglycinediacetic acid”).

If desired, other additives can also be included in aqueous polymersolutions described herein, such as biocides, oxygen scavengers, andcorrosion inhibitors.

Variants of the methods described above can also be used to prepareaqueous polymer solutions that include biopolymers, such aspolysaccharides (e.g., xanthan gum, scleroglucan, guar gum, derivativesthereof including one or more chemical modifications to the backbone ofthese polymers, and blends thereof). These methods can compriseproviding a liquid polymer (LP) composition comprising one or morebiopolymers; and combining the LP composition with an aqueous fluid in asingle stage mixing process described above to provide the aqueouspolymer solution, wherein the aqueous polymer solution comprises aconcentration of biopolymer of from 50 to 15,000 ppm; and wherein theaqueous polymer solution has a filter ratio of 1.5 or less at 15 psiusing a 1.2 μm filter.

In methods used to prepare aqueous polymer solutions that includebiopolymers, the single stage mixing process can comprise applying aspecific mixing energy of at least 0.10 kJ/kg to the LP composition andthe aqueous fluid.

In some of these embodiments, the single stage mixing process cancomprise applying a specific mixing energy of at least 0.10 kJ/kg (e.g.,at least 0.25 kJ/kg, at least 0.50 kJ/kg, at least 0.75 kJ/kg, at least1.0 kJ/kg, at least 1.5 kJ/kg, at least 2.0 kJ/kg, at least 2.5 kJ/kg,at least 3.0 kJ/kg, at least 3.5 kJ/kg, at least 4.0 kJ/kg, at least 4.5kJ/kg, at least 5.0 kJ/kg, at least 6.0 kJ/kg, at least 7.0 kJ/kg, atleast 8.0 kJ/kg, at least 9.0 kJ/kg, at least 10 kJ/kg, at least 11kJ/kg, at least 12 kJ/kg, at least 13 kJ/kg, at least 14 kJ/kg, at least15 kJ/kg, at least 16 kJ/kg, at least 17 kJ/kg, at least 18 kJ/kg, or atleast 19 kJ/kg) to the LP composition and the aqueous fluid. In some ofthese embodiments, the single stage mixing process can comprise applyinga specific mixing energy of 20 kJ/kg or less (e.g., 19 kJ/kg or less, 18kJ/kg or less, 17 kJ/kg or less, 16 kJ/kg or less, 15 kJ/kg or less, 14kJ/kg or less, 13 kJ/kg or less, 12 kJ/kg or less, 11 kJ/kg or less, 10kJ/kg or less, 9.0 kJ/kg or less, 8.0 kJ/kg or less, 7.0 kJ/kg or less,6.0 kJ/kg or less, 5.0 kJ/kg or less, 4.5 kJ/kg or less, 4.0 kJ/kg orless, 3.5 kJ/kg or less, 3.0 kJ/kg or less, 2.5 kJ/kg or less, 2.0 kJ/kgor less, 1.5 kJ/kg or less, 1.0 kJ/kg or less, 0.75 kJ/kg or less, 0.50kJ/kg or less, or 0.25 kJ/kg or less) to the LP composition and theaqueous fluid.

In some of these embodiments, the single stage mixing process cancomprise applying a specific mixing energy to the LP composition and theaqueous fluid ranging from any of the minimum values described above toany of the maximum values described above. For example, in some of theseembodiments, the single stage mixing process can comprise applying aspecific mixing energy of from 0.10 kJ/kg to 20 kJ/kg (e.g., from 0.10kJ/kg to 10 kJ/kg, from 1.0 kJ/kg to 20 kJ/kg, from 1.0 kJ/kg to 15kJ/kg, from 1.0 kJ/kg to 10 kJ/kg, or from 5.0 kJ/kg to 15 kJ/kg) to theLP composition and the aqueous fluid.

Variants of the methods described above can also be used to prepareaqueous polymer solutions from solid polymer powders, such as solidpolyacrylamide polymer powders. These methods can comprise combining thesolid polymer powder with an aqueous fluid in a mixing process toprovide the aqueous polymer solution, wherein the aqueous polymersolution comprises a concentration of polymer of from 50 to 15,000 ppm;and wherein the aqueous polymer solution has a filter ratio of 1.5 orless at 15 psi using a 1.2 μm filter.

In methods used to prepare aqueous polymer solutions from solid polymerpowders, the mixing process can comprise applying a specific mixingenergy of at least 1.0 kJ/kg to the solid polymer powder and the aqueousfluid.

In some of these embodiments, the mixing process can comprise applying aspecific mixing energy of at least 1.0 kJ/kg (e.g., at least 1.25 kJ/kg,at least 1.5 kJ/kg, at least 2.0 kJ/kg, at least 2.5 kJ/kg, at least 3.0kJ/kg, at least 3.5 kJ/kg, at least 4.0 kJ/kg, at least 4.5 kJ/kg, atleast 5.0 kJ/kg, at least 6.0 kJ/kg, at least 7.0 kJ/kg, at least 8.0kJ/kg, at least 9.0 kJ/kg, at least 10 kJ/kg, at least 11 kJ/kg, atleast 12 kJ/kg, at least 13 kJ/kg, at least 14 kJ/kg, at least 15 kJ/kg,at least 16 kJ/kg, at least 17 kJ/kg, at least 18 kJ/kg, or at least 19kJ/kg) to the solid polymer powder and the aqueous fluid. In some ofthese embodiments, the mixing process can comprise applying a specificmixing energy of 20 kJ/kg or less (e.g., 19 kJ/kg or less, 18 kJ/kg orless, 17 kJ/kg or less, 16 kJ/kg or less, 15 kJ/kg or less, 14 kJ/kg orless, 13 kJ/kg or less, 12 kJ/kg or less, 11 kJ/kg or less, 10 kJ/kg orless, 9.0 kJ/kg or less, 8.0 kJ/kg or less, 7.0 kJ/kg or less, 6.0 kJ/kgor less, 5.0 kJ/kg or less, 4.5 kJ/kg or less, 4.0 kJ/kg or less, 3.5kJ/kg or less, 3.0 kJ/kg or less, 2.5 kJ/kg or less, 2.0 kJ/kg or less,1.5 kJ/kg or less, or 1.25 kJ/kg or less) to the solid polymer powderand the aqueous fluid.

In some of these embodiments, the mixing process can comprise applying aspecific mixing energy to the solid polymer powder and the aqueous fluidranging from any of the minimum values described above to any of themaximum values described above. For example, in some of theseembodiments, the mixing process can comprise applying a specific mixingenergy of from 1.0 kJ/kg to 20 kJ/kg (e.g., from 1.0 kJ/kg to 15 kJ/kg,from 1.0 kJ/kg to 10 kJ/kg, from 1.25 kJ/kg to 20 kJ/kg, from 1.25 kJ/kgto 15 kJ/kg, from 1.25 kJ/kg to 10 kJ/kg, from 1.5 kJ/kg to 20 kJ/kg,from 1.5 kJ/kg to 15 kJ/kg, or from 1.5 kJ/kg to 10 kJ/kg) to the solidpolymer powder and the aqueous fluid.

In some of these embodiments, the mixing process can comprise a singlestage mixing process described herein. In some cases, the solid powderpolymer can be a synthetic polymer, such as a polyacrylamide, apartially hydrolyzed polyacrylamide, a hydrophobically-modifiedassociative polymer, a 2-acrylamido 2-methylpropane sulfonic acid or asalt thereof, an N-vinyl pyrrolidone, a polyacrylic acid, a polyvinylalcohol, or a mixture thereof.

Methods of Use

The aqueous polymer solutions described herein can be used in a varietyof oil and gas operations, including an EOR operation (e.g., an improvedoil recovery (IOR) operation, a polymer flooding operation, an APflooding operation, a SP flooding operation, an ASP flooding operation,a conformance control operation, or any combination thereof). Moreover,the aqueous polymer solutions described herein can be used in a varietyof oil and gas operations, including a hydraulic fracturing operation,as a drag reducer that reduces friction during transportation of a fluidin a pipeline, or any combination thereof. Transportation of a fluid ina pipeline can refer to any movement of a fluid through a conduit orpipe. As such, transportation of a fluid in a pipeline includes, forexample, the pipeline transport of fluids as well as passage of fluidsthrough pipes such as wellbores during the course of an oil recoveryoperation. The aqueous polymer solutions can even be used in watertreatment operations associated with oil and gas operations.

In one embodiment, the aqueous polymer solution can be used as aninjection fluid. In another embodiment, the aqueous polymer solution canbe included in an injection fluid. In another embodiment, aqueousinverted polymer solution can be used as a hydraulic fracturing fluid.In another embodiment, the aqueous polymer solution can be included in ahydraulic fracturing fluid. In another embodiment, the aqueous polymersolution can be used as a drag reducer that reduces friction duringtransportation of a fluid in a pipeline. In another embodiment, theaqueous polymer solution can be included in a drag reducer that reducesfriction during transportation of a fluid in a pipeline. In short, incertain embodiments, the aqueous polymer solutions described herein canbe used in hydrocarbon recovery.

Methods of hydrocarbon recovery can comprise providing a subsurfacereservoir containing hydrocarbons therewithin; providing a wellbore influid communication with the subsurface reservoir; preparing an aqueouspolymer solution using the methods described above; and injecting theaqueous polymer solution through the wellbore into the subsurfacereservoir. For example, the subsurface reservoir can be a subseareservoir and/or the subsurface reservoir can have a permeability offrom 10 millidarcy to 40,000 millidarcy.

The wellbore in the second step can be an injection wellbore associatedwith an injection well, and the method can further comprise providing aproduction well spaced-apart from the injection well a predetermineddistance and having a production wellbore in fluid communication withthe subsurface reservoir. In these embodiments, injection of the aqueouspolymer solution can increase the flow of hydrocarbons to the productionwellbore.

In some embodiments, methods of hydrocarbon recovery can further includea recycling step. For example, in some embodiments, methods ofhydrocarbon recovery can further comprise producing production fluidfrom the production well, the production fluid including at least aportion of the injected aqueous polymer solution; and combining theproduction fluid to with additional LP composition, for example, to forma second aqueous polymer solution. The second aqueous polymer solutioncan then be injected into at least one wellbore (e.g., an injectionwell, the same wellbore discussed in the second step or a differentwellbore, etc.). Thus, in some embodiments, the aqueous polymer solutionis included in an injection fluid.

The wellbore in the second step can be a wellbore for hydraulicfracturing that is in fluid communication with the subsurface reservoir.Thus, in one embodiment, the aqueous polymer solution injected in thefourth step functions as a drag reducer that reduces friction duringinjection in the fourth step. By doing so, the aqueous polymer solutionis used as a drag reducer that reduces friction during transportation ofa fluid (e.g., the hydraulic fracturing fluid) in a pipeline (e.g., thewellbore or components thereof). In another embodiment, the aqueouspolymer solution is included in a hydraulic fracturing fluid.

By way of non-limiting illustration, examples of certain embodiments ofthe present disclosure are given below.

EXAMPLES

Methods and Materials

Brine Composition and Hydration.

A synthetic brine was used as base brine. The synthetic brine includedthe following: Na⁺, Ca²⁺, Mg²⁺, Cl⁻, and a TDS of about 15,000 ppm asshown in Table 1. Since the neat liquid polymer (LP) was provided as anoil-continuous polymer dispersion with an activity of 50%, the LPpolymer was inverted and diluted to target concentration of 2000 ppm inthe synthetic brine by mixing at 500 rpm using an overhead mixer. In thelaboratory, 50% neat liquid polymer was inverted to 1% LP solution inthe synthetic brine using the overhead mixer at 500 rpm for 2 hours.Then, the 1% inverted LP solution was diluted to the targeted 0.2% LPsolution in the synthetic brine using the overhead mixer at 500 rpm for2 hours to 24 hours. 50% neat liquid polymer was also directly invertedto the target concentration of 0.2% LP polymer in the synthetic brineusing the overhead mixer for 3 hours to 24 hours.

TABLE 1 Composition of the synthetic seawater brine used in theexamples. Ions (ppm) Synthetic seawater brine Na+ 5,048 Ca++ 569 Mg++210 Cl− 9,403 TDS 15,230

Filter Ratio Test.

Polymer filter ratio tests were carried out to identify theeffectiveness of the polymer mixing (hydration/dilutions) in the sourcebrine and therefore provide an indication of how effectively thatpolymer can be injected through a porous medium without any plugging orretention. The filter ratio (FR) of the polymer solutions was determinedusing the standard procedure described, for example, in Koh, H.Experimental Investigation of the Effect of Polymers on Residual OilSaturation. Ph.D. Dissertation, University of Texas at Austin, 2015;Levitt, D. The Optimal Use of Enhanced Oil Recovery Polymers UnderHostile Conditions. Ph.D. Dissertation, University of Texas at Austin,2009; and Magbagbeola, O. A. Quantification of the Viscoelastic Behaviorof High Molecular Weight Polymers used for Chemical Enhanced OilRecovery. M. S. Thesis, University of Texas at Austin, 2008, each ofwhich is hereby incorporated by reference in its entirety.

Briefly, a 300 ml solution of 2000 ppm inverted LP solution in syntheticbrine was filtered through a 5.0 μm and 1.2 μm ISOPORE™ polycarbonatefilter with a diameter of 47 mm at 15 psi (plus or minus 10% of 15 psi)pressure and ambient temperature (25° C.). As expressed in the formulabelow, the FR was calculated as the ratio of the time for 180 to 200 mlof the polymer solution to filter divided by the time for 60 to 80 ml ofthe polymer solution to filter.

${FR} = \frac{{{\,^{t}200}\mspace{14mu}{ml}} - {{\,^{t}180}\mspace{14mu}{ml}}}{{{\,^{t}80}\mspace{14mu}{ml}} - {{\,^{t}60}\mspace{14mu}{ml}}}$Ideally, a filtration ratio of 1.0 indicates that the polymer solutionis homogeneous and hydrated so as to flow through accessible porethroats without any plugging. For the composition to qualify for furthertesting, the composition was required to exhibit a FR of less than orequal to 1.2 through both filters. As the 1.2 FR was a strict laboratoryrequirement for polymer qualification, clean, laboratory-grade filteredwater was used when necessary.

Rheological Measurements.

For all polymers, the basic rheology in terms of viscosity versusconcentration, viscosity versus shear rate, neat polymer viscosity weremeasured. Steady-state shear viscosities were measured in the range of0.1 s-1 to 1000 s-1 at 25° C., and 31° C. using double-wall couettegeometry with a TA Instruments ARES-G2 rheometer.

Long Term Injectivity Experiments.

Polymer injectivity tests were performed separately using 2000 ppmpolymer solution in a 2000 mD Bentheimer sandstone at 31° C. Briefly,the cores were setup vertically with water being injected from thebottom. The initial permeability was measured with synthetic brine,followed by tracer tests to ensure that cores were acceptablyhomogeneous. On completion of the tracer tests, 2000 ppm polymersolution was injected at a rate of approximately 5 ft/day for more than25 PV to establish plugging tendencies. The differential pressure dropbetween inlet and outlet (i.e., across the whole core) was measuredusing Rosemount differential pressure transducers. In some cases,pressure taps near the inlet measured face plugging.

Oil Recovery Experiments.

Oil recovery experiments were performed using 2000 ppm LP using anapproximately 5000 mD unconsolidated-sand pack at 31° C. The flow ratewas set at 0.5 mL/min, corresponding to ˜4 ft/day. The differentialpressure drop between inlet and outlet was measured using Rosemountdifferential transducers. A viscous crude oil (80 cP at 31° C.) wasselected in this experiment.

Polymer Loop Yard Tests.

Upon successful mixing and performance in laboratory scale, polymer loopyard tests were performed to validate larger scale mixing andperformance at semi-field scale using multiple configurations of staticmixers. Liquid polymer was mixed through a conventional two stage mixingprocess as well as a single stage mixing process. The performance of theinverted liquid polymers through static mixers was investigated bymeasuring FR, viscosity and short-term injectivity tests on-site.

Field Portable Measurement Unit (PMU).

A portable measurement unit (PMU) was used for on-site surveillance infield. The PMU was configured to measure polymer rheology, filterabilityand long-term core injectivity. Polymer rheology was measured using aseries of capillary tubes with pressure measurements. Filterability wasmeasured through a 1.2 um filter at 15 psi with pre-filtration to removelarge oil droplets and suspended solids. Filterability was also measuredwithout pre-filtration. Finally, long-term injectivity was measuredusing an epoxy-coated Bentheimer core with a pressure tap to determineface-plugging. The PMU allowed for native injection fluids to bemonitored and analyzed under anaerobic conditions to ensure theproject's success despite the challenges of being in a remote site.

Results and Discussion

FR Test:

FIG. 7 shows a plot of the FR test performed for an inverted polymersolution using a 1.2 micron filter with a diameter of 47 mm at 15 psipressure and 25° C. temperature. As shown in FIG. 7 and Table 2, theinverted LP solution (2000 ppm polymer) passes through 1.2 micron filterwith a FR of less than or equal to 1.5. More specifically, FIG. 7illustrates a FR of 1.2 or less. Even more specifically, FIG. 7illustrates a FR of 1.13. This result indicates the improvedfilterability of the inverted polymer solution.

Viscosity Measurement:

FIG. 8 shows a viscosity plot for a wide range of shear rates for aninverted polymer solution (2000 ppm polymer in synthetic brine, measuredat 31° C.). The viscosity of the inverted polymer solution illustrates atypical shear-thinning behavior in the wide range of shear rate. Theviscosity is measured as 24 cP at 10 s-1 and 31° C.

Injectivity Test:

The inverted polymer solution was injected into outcrop Bentheimersandstones. The purpose of the polymer injection was to evaluate theinjectivity of the inverted polymer solution in the porous medium.Around 30 PV of 2000 ppm LP polymer in synthetic brine was injected intoBentheimer sandstone at flow rate of 0.5 ml/min corresponding to 6ft./day at the temperature of 31° C. As shown in FIG. 6, the pressuredrop for the inverted polymer solution reaches steady-state after 2 porevolume (PV) which indicates no plugging. The corresponding relativepermeability history is also plotted in FIG. 6. The relativepermeability of the inverted polymer solution after 28 PV was ˜1 whichconfirms core plugging.

Oil Recovery Experiment:

The ability of the inverted polymer solution to displace oil and improverecovery was tested in Bentheimer sandstone in the presence of crudeoil. A viscous crude oil (80 cP at 31° C.) was chosen for the test. Theinverted polymer solution was injected at the end of water flooding inseparate core flooding experiments. The oil recovery and pressure dropis plotted in FIG. 10. As seen in Figures, oil recovery improves as theinverted LP solution is injected while pressure drop for LP injectionshows steady-state and low at the end of the experiment. Thesteady-state low pressure drop for LP solution at the end of theexperiment indicates improved behavior as the LP solution do not plugthe core during oil recovery

TABLE 2 Summary of properties of inverted LP composition. 5 μm filter(15 psi, 1.2 μm filter 25° C.) (15 psi, 25 C.) Polymer Time to Time toViscosity Poly- Concentration 200 g 200 g (cP) @ 31° C. mer (ppm) F.R(min) F.R (min) 10 s⁻¹ LP 2000 1.00 5.0 1.13 27 22 2000 1.01 4.4 1.19 2521 2000 1.04 5.7 1.18 24 25

Validation of Filtration Test and Viscosity Measurements UsingPilot-Scale LP Samples:

Additional filtration ratio test and viscosity measurements wereperformed using larger-scale produced samples. These include pilot-scaleand commercial field-scale samples compared with previous lab-scalemanufactured samples. The results of filtration ratio and viscositymeasurement have been summarized in Table 3. 2000 ppm inverted polymersolutions were prepared using different pilot-scale batches of LPsolutions (M1 through M5) and filtration tests were performed asdescribed above. The average activity of neat polymer is measured as50.9±0.9%. Viscosity of neat polymer is 207±148 cP at room temperature.2000 ppm of the inverted polymer solution shows a viscosity of 21±3 cPat 10 sec-1, 31° C.

The viscosity yield as a function of concentration of polymer used wasmeasured at 31° C. FIG. 11 shows the viscosity yield curve as a functionof concentration. Mother solution of 10,000 ppm concentrate was preparedfrom 52% active neat polymer. From this mother solution, appropriatedilutions were made and viscosities measured between 0.1 sec⁻¹ and 1000sec⁻¹. The viscosity values in FIG. 11 correspond to a shear rate of 10sec⁻¹. At a concentration of 2000 ppm inverted polymer solution, theviscosity is about 23 cP and the viscosity yield of 10,000 ppm invertedpolymer solution is approximately 900 cP. FIG. 12 shows the polymerviscosity as a function of shear rate. As shown in FIG. 12 shearthinning behavior of polymer solutions was observed. As the polymerconcentrations increased, the shear thinning behavior changed from lessshear thinning to more shear thinning.

TABLE 3 Summary of filtration and viscosity data using pilot-scalesamples. Viscosity (cP) @ 10 s−1 Filtration Ration Test @ 15 psi, 25 C.Sample Activity Neat (25 C.) 2k ppm (31 C.) F.R. (5 um) time to 200 g(m) F.R. (1.2 um) time to 200 g (m) S-1 52.4% 179 25 1.04 5.7 1.18 24 221 5 1.13 27 21 1.01 4.4 1.19 25 M-1 52.1% 152 26 1.05 6.2 1.32 28.4 1.036.0 1.22 25.2 1.43 30.0 M-2 51.8% 128 25 1.04 6.1 1.44 30.8 M-3 50.3%104 24 1.04 6.3 1.24 29.4 1.31 27.4 16 1.34 13.2 20 1.50 21.0 M-5 50.5%101 21 1.04 5.0 1.24 24.0 1.39 26.2 19 1.22 14.4 19 1.30 16.5 M-6 51.2%107 21 1.03 4.8 1.31 26.0 1.37 27.8 18 1.21 16.0 PL#5 50.0% 241 22 1.1316.0 PL#6 50.0% 252 20 1.27 16.0 TL#2 50.0% 599 24 1.24 20.5 Mean 207 211.04 5.51 1.28 23.1 Std. Dev 148 3 0.02 0.66 0.10 5.5

2000 ppm inverted polymer solutions were prepared using differentpilot-scale batches of LP solutions (M1 through M5) and filtration testswere performed as described above. FIGS. 13A and 13B show the results offiltration ratio tests performed with different pilot-scale batches ofLP solutions using a 5 micron filter (FIG. 13A) and 1.2 micron filter(FIG. 13B) at 15 psi. As shown in FIGS. 13A and 13B, the LP solutionsproduce a FR of 1.04+/−0.02 for a 5 micron filter and 1.28+/−0.1 for a1.2 micron filter.

FIG. 14 shows a long-term injectivity test of single phase invertedpolymer solution in a core. The core included a pressure tap two inchesfrom the face, providing a pressure differential across the injectionface of the core. As shown in FIG. 14, the steady-state pressure dropshowed no significant signal consistent with plugging of the sandstonecore. Analysis of the pressure drop during the post-water flood alsoshowed no plugging.

To verify the long-term injectivity performance of the inverted LPsolutions, the relative permeability of the single phase polymer floodwas normalized using methods known in the art (see SPE 179657, SPE IORsymposium at Tulsa 2016, which is incorporated herein by reference inits entirety). FIG. 15A shows the relative plugging when the results arenormalized for each section with total pore volumes injected for aconventional emulsion polymer. These results indicate that the pluggingrate is faster near the injection face compared to subsequent sectionsof the core. In contrast, as shown in FIG. 15B, the inverted LPsolutions do not exhibit any significant signs of plugging.

FIG. 16 shows the permeability Reduction Factor (Rk) and Normalized SkinFactor, s/ln(r_(s)/r_(w)) vs. filtration ratio at 1.2 μm (FR 1.2). Asshown in FIG. 16, Rk and skin factor both increase when FR is greaterthan 1.5. These results suggest that injection of a polymer solutionwith a FR greater than 1.5 plugs the core, while injection of a polymersolution with a FR of 1.5 or less causes no plugs to the core.

Polymer Loop Yard Tests:

With polymer mixing and performance in laboratory conditions validated,the next step was to evaluate the mixing efficiency of the neat solutionin brine to a final 2000 ppm polymer concentration in larger scale yardtests. The goal of the yard tests was to demonstrate that acceptableviscosity yield and filtration ratio could be achieved using single stepconfiguration mixers and multi-step configuration mixers (with andwithout dynamic mixers) as described in FIGS. 1 and 2.

Experimental results using a single step mixer configuration aresummarized in Table 4 and experimental results using a multi-step mixerconfiguration are summarized in Table 5. Each experiment was performedusing different size static mixer elements and different configurationsincluding dynamic mixer, different flow rate and different ratio of neatpolymer and brine. The samples were collected after each run, andfiltration tests and viscosity measurements were performed to verify thehydration of the LP including inversion and dilution through thedesigned mixing system.

TABLE 4 Summary of polymer loop yard test - example of single stepmixing. Filtration Pressure Mixer Flow Viscosity Time across the Mixing1st stage 2nd stage rate Velocity Dynamic (cP, 31 C.) FR (min, mixer Run# Scheme (Inversion) (Dilution) gpm (m/s) mixer 7.3 s−1 10 s−1 (1.2 μm)200 g) (psi) S-1 Single 1″ϕ:15 elements 30 3.7 Y 21.7 18.8 1 120 120step S-2 Single 1″ϕ:15 elements 30 3.7 N 21.2 19.5 1.14 83 125 step S-3Single 2″ϕ:15 elements 95 3 Y 26.7 23.3 1 120 120 step S-4 Single 2″ϕ:15elements 95-100 3.1 N 26.7 23.6 1.07 100 180 step

TABLE 5 Summary of polymer loop yard test - example of multistep mixing.Filtration Mixer Flow Viscosity Time Pressure Mixing 1st stage 2nd stagerate Velocity Dynamic (cP, 31 C.) FR (min, across the Run # Scheme(Inversion) (Dilution) gpm (m/s) mixer 7.3 s−1 10 s−1 (1.2 μm) 200 g)mixer (psi) M-1 Two step 1″ϕ:15 2″ϕ:15 125-130 3.4/3.9 N 26.2 23 1.3 95140 elements elements M-2 Two step 1″ϕ:15 2″ϕ:15 125 3.4/3.9 Y 23 20.11.13 99 140 elements elements M-3 Two step 1″ϕ:15 2″ϕ:15 100 2.5/3.1 Y23 20 1.2 85 100 elements elements

As shown in FIG. 17, viscosity yields were measured above 20 cP in bothmulti-step (two) mixing configuration and single step mixingconfiguration with and without the dynamic mixer. This shows that the LPproperly hydrates through the static mixers in both a single-step or inmulti-step configuration. FIGS. 18A and 18B show the viscosity yield asa function of pressure drop across the static mixers (FIG. 18A) andfiltration ratio as a function of pressure drop across the static mixers(FIG. 18B). To hydrate the LP and provide a suitable viscosity yield andfilterability, a FR of 1.5 or less at 1.2 micron should be used.

Overall, the polymer loop yard tests demonstrate that successfulviscosity yields can be achieved with a suitable filtration ratio usingeither a single step or multi-step mixing process. Furthermore,injectivity experiments through surrogate rock showed no appreciableplugging behavior.

Development of Mixing Configurations for Field-Scale Applications:

Traditionally, aqueous polymer solutions are prepared from LPcompositions using a two-stage mixing process. An example two stagemixing process is schematically illustrated in FIG. 19. In the first(inversion) stage, LP polymer composite was mixed with a slipstream ofthe injection water to be inverted to a mother solution of 10,000 ppm.The mother solution concentration was controlled by varying theslipstream flow using a globe valve on the water injection flowline. Theinversion mixer is a static in-line mixer with a recommendeddifferential pressure range of 3-10 barg. Either a 3″ or 4″ mixer couldbe selected to maintain the recommended differential pressure across theanticipated range of injection flowrates. In the second (dilution) stagethe mother solution was mixed with the main injection stream to achievea polymer solution concentration of 1750-2000 ppm. The dilution mixerwas a static in-line mixer with a 1˜3 barg pressure drop. The polymersolution concentration was controlled by varying the polymer injectionpump stroke length.

Field trials were conducted using this two-stage mixing process, but hadto be suspended due to irreversible loss of injectivity. Studiesdemonstrated that the loss of injectivity was due to near wellboredamage mechanisms associated with the hPAM liquid emulsion preparedusing the two-stage mixing process. These problems were traced back tocertain operational issues associated with the two-stage mixing processdescribed above, including operation of the inversion mixer outside ofits preferred operating envelope, and blockage of inversion mixer due tooverinj ection of polymer.

To remedy these issues, an alternative mixing configuration wasdeveloped which eliminated the two-stage mixing process while stillachieving the desired FR specification (an FR of 1.5 or less at 15 psiusing a 1.2 μm filter) and viscosity target. This simpler, single stagemixing configuration significantly reduced the possibility ofout-of-specification injection during normal injection.

The single stage mixing configuration is schematically illustrated inFIG. 20. The system included two mixers operating in series, andeliminated the requirement for a two-stage inversion/dilution process.LP composition was introduced to the water injection stream via a 6″dynamic mixer. A 6″ SCH 120 static in-line Sulzer SMX mixer wasinstalled directly downstream from the dynamic mixer. The static mixerincluded 12 elements oriented as shown in FIG. 21. The 6″ mixer sizingwas selected to facilitate injection of a design rate of 30,000 bpd at1800 ppm. The mixing configuration was sized such that fluid velocitywas limited to less than ca. 3.8 m/s to avoid unnecessary shearing ofthe solution while maintaining a reasonable pressure drop.

Performance of Single-Stage Mixing Process in Yard Trial and Field PilotApplications:

Table 6 includes the viscosity data and filtration data for liquidpolymer solution prepared using an overhead mixer in a laboratory as areference. Tables 7 and 8 show the mixing condition and results ofliquid polymer mixing using the single stage mixing process at ayard-scale. Table 9 shows the mixing condition and results of liquidpolymer mixing using the single stage mixing process in a field pilotapplication.

TABLE 6 Results of Lab experiments for various samples mixed in overheadmixer. Viscosity (cP) Filtration Ratio 2000 ppm F.R. time to E/M Sample(31° C.) (1.2 μm) 200 g (m) (kJ/kg) S-1 25 1.18 24 1.10 22 1.13 27 1.1021 1.19 25 1.10 M-1 26 1.32 28.4 1.10 1.22 25.2 6.58 M-2 25 1.44 30.81.10 M-3 24 1.24 29.4 1.10 CA-1 24 1.0 15 0.55 SE-1 18 1.0 45 0.27 SE-224 1.0 60 0.14

TABLE 7 Summary of yard test data: Example of single stage mixing.Filtration Total ratio Static Mixer Field flow Pressure time ViscosityMixing 1st stage 2nd stage Dynamic flow rate rate drop (psi) FR_(1.2)(min, (cP) E/M Run # Scheme (Inversion) (Dilution) mixer, DM (bbl/day)gpm DM SM (1.2 μm) 200 g) 7.3 s⁻¹ 10 s⁻¹ kJ/kg S-1 Single Step 2″ϕ:15elements N 40,000 148 154.8 1.31 120 34.4 30.6 1.07 S-2 Single Step2″ϕ:15 elements N 30,000 111 87.6 1.4 165 32 29.3 0.60 S-3 Single Step2″ϕ:15 elements N 30,000 111 88 1.19 127 34.4 31.4 0.61 S-4 Single Step2″ϕ:15 elements N 15,000 49 17.9 2.22 225 31.8 29.3 0.12 S-5 Single Step2″ϕ:15 elements N 15,000 49 17.7 1.3 144 35.6 31.9 0.12 S-6 Single Step2″ϕ:15 elements N 10,000 32.69 8.2 1.9 127 34.7 31.7 0.06 S-7 SingleStep 2″ϕ:15 elements N 7,500 24.5 4.7 2.95 164 37.1 33 0.03 S-8 SingleStep 2″ϕ:15 elements N 5,000 16.8 2.2 2.65 225 35.1 32.2 0.02 S-9 SingleStep 2″ϕ:15 elements Yes (2″ϕ) 40,000 149 25.4 154.7 1.12 120 34.7 32.41.07 S-10 Single Step 2″ϕ:15 elements Yes (2″ϕ) 30,000 112 14.4 87.71.13 115 37 33.51 0.60 S-11 Single Step 2″ϕ:15 elements Yes (2″ϕ) 15,00050 3.1 19.8 1.24 128 36.3 33.5 0.14 S-12 Single Step 2″ϕ:15 elements Yes(2″ϕ) 10,000 33.5 1.5 9.6 1.43 186 36.9 33.6 0.07 S-13 Single Step2″ϕ:15 elements Yes (2″ϕ) 7,500 25 0.9 5.9 1.76 197 39.3 34.9 0.04 S-14Single Step 2″ϕ:15 elements Yes (2″ϕ) 5,000 16.7 0.6 3 2.31 153 36.233.3 0.02 S-15 Single Step 3″ϕ:15 elements Yes (3″ϕ) 30,000 242 22.2104.9 1.25 119 30.8 18.7 0.72 S-16 Single Step 3″ϕ:15 elements Yes (3″ϕ)15,000 111 4.6 22.9 1.1 161 34.8 17.7 0.16 S-17 Single Step 3″ϕ:15elements Yes (3″ϕ) 10,000 69 1.9 9.6 1.08 211 35.2 17.7 0.07 S-18 SingleStep 3″ϕ:15 elements Yes (3″ϕ) 7,500 53 2.6 5.5 1.62 160 35.8 18.3 0.04S-19 Single Step 3″ϕ:15 elements Yes (3″ϕ) 5,000 34 0.5 2.6 1.89 23336.7 18.4 0.02

TABLE 8 Summary of yard test data: Example of two stage mixing.Filtration Total Pressure ratio Mixer Dynamic Field flow flow drop (psi)time Viscosity Mixing 1st stage 2nd stage mixer, rate rate 1st 2ndFR_(1.2) (min, (cP) E/M Run # Scheme (Inversion) (Dilution) DM (bbl/day)gpm DM SM SM (1.2 μm) 200 g) 7.3 s⁻¹ 10 s⁻¹ kJ/kg T-1 Two 1″ϕ:15 2″ϕ:15N 30,000 111 46 159 1 179 20 19 1.41 step elements elements T-2 Two1″ϕ:15 2″ϕ:15 Yes (1″ϕ) 30,000 110 8 60 158 1 650* 18 17 1.51 stepelements elements T-3 Two 1″ϕ:15 2″ϕ:15 Yes (1″ϕ) 15,000 49 0 8 53 2 10536 34 0.42 step elements elements

TABLE 9 Summary of field test data: Example of single step mixing. MixerPressure Viscosity Mixing 1st stage 2nd stage Field dlow rate dropFR_(1.2) (cP) E/M Run # Scheme (Inversion) (Dilution) (bbl/day) Bar psi1.2 μm 7.3 s⁻¹ 10 s⁻¹ kJ/kg T-1 Single step 6″ϕ:12 elements 14780 2.4 401.1 20 19 0.27 T-2 Single step 6″ϕ:12 elements 19963 4.3 71 1.4 18 170.49 T-3 Single step 6″ϕ:12 elements 24768 6.5 106 1.4 36 34 0.73 T-4Single step 6″ϕ:12 elements 17914 3.5 57 1.4 36 34 0.39 T-5 Single step6″ϕ:12 elements 10630 1.3 21 1.4 36 34 0.15

The ability of the single stage mixing process to meet reservoirspecifications was assessed at yard scale conditions. FIG. 22 shows theviscosity yield achieved using various mixer configurations. To meetreservoir specifications, a polymer solution viscosity of 32 cP (@ 10s⁻¹ and 20° C.) was expected. For the two-stage mixing process, theaverage viscosity was limited to ca. 20 cP. However, the single stagemixing process was able to ensure a viscosity yield >32 cP across alltested mixer sizes.

FIG. 23 shows that DP and FR varied with injection rate when using thesingle stage mixing process at 2″ yard test scale. The dotted linesindicate the pressure drop (DP) across the static mixer with and withoutthe dynamic mixer. Solids symbols indicate the filtration ratio of theinverted aqueous polymer solutions at each corresponding injection rate.Filtration ratio was measured at 1.2 micron filter under 15 psi. Thesingle stage mixing process also produced inverted aqueous polymersolutions that met the FR specification of ≤1.5 at an injection rateequivalent to ca. 30,000 bpd in a 6″ system. This performance wassustained as the velocity across the mixers was reduced to theequivalent of 10,000 BPD.

FIG. 24 shows the relationship between DP and fluid velocity for thecombined dynamic/static mixer configuration with 1″, 2″ and 3″ units.The results associated with the three sizes show a strong correlationand demonstrate that a velocity of greater than ca. 1.0 m/s provides aminimum DP of ca. 1.0 bar over the two mixers.

FIG. 25 shows the relationship between DP and FR. Maintaining a DP ofgreater than 1 bar across the mixing configuration ensured that the <1.5FR specification was met.

FIGS. 24 and 25 also demonstrate the impact of removing the dynamicmixer. At high flowrates, the impact is negligible but below ca. 12,500bpd there was insufficient pressure drop to achieve the FRspecification.

From the analysis above; it was concluded that, for the single stagemixing process: (1) an FR of <1.5 could be achieved at a maximuminjection solution velocity of 3.8 m/s to avoid excessive shearing; and(2) solution injection velocity could be maintained at >1.0 m/s toensure sufficient mixing and achieve an FR≤1.5.

The field design was based on 6″ mixers; however, strategically locatedRemovable Spool Pieces (RSPs) were incorporated as shown in FIG. 20 toallow mixers to be changed out to increase turndown capability. The useof RSPs also provided flexibility in the number of mixer elements andtherefore the differential pressure achieved.

In addition to meeting key reservoir FR and viscosity specifications,the proposed single stage mixing configuration proved robust inpreventing mixer blockages. In an offshore environment, operationalexcursions leading to over injection of polyacrylamide can occur.Previous excursions in the oil field have led to plugging of theinversion mixer. Although, this plugging can be cleared by increasingwater flow through the inversion mixer, there is no alternative routingavailable to prevent injection of the resulting highly concentratedpolymer slug. Furthermore, installation of alternate disposal facilitiesis impractical.

In the yard environment, water injection rates equivalent to 5000 bpdwere mixed with hPAM-based liquid polymer to form a ca. 7000 ppmsolution. Even though the resulting solution failed to meet FR andviscosity specifications, no mixer blockages were observed. Bycomparison, field and yard scale experience has demonstrated that mixingthe same 7000 ppm solution using a two-stage mixer configuration wouldimmediately result in mixer blockages. It is believe that by disposingof the two-stage mixing, the process fluid is restricted to a singleflow path, thereby increasing available backpressure and reducing thefrequency of blockages.

Analysis of Specific Mixing Energy:

The combination of target viscosity effects and filtration ratioimprovement to evaluate mixing energy is possible via the application ofSpecific Mixing Energy (SME):

${E\text{/}M} = {\frac{k\;\omega^{2}t}{V}\left\lbrack \frac{kJ}{kg} \right\rbrack}$where k is a constant (6.4×10⁻¹² kNm/kg*m³/rpm), ω is the rotationalspeed (rpm), t is the mixing time of the polymer solution in the blender(min) and V is the volume of solution (m3). The constant and values wererecalculated for the current study from the values provided in theliterature (see SPE 25147-PA and SPE-15578, each of which isincorporated herein by reference in its entirety).

SME attempts to quantify the amount of energy consumed during theprocess of mixing a fluid. As such, SME can be used to find trendsagainst key fluid performance parameters.

Analysis of the equation for SME demonstrates that equivalent mixingenergy values can be achieved by increasing and decreasingsimultaneously the upper terms in the equation. For instance, in thecase of field equipment, the same value of mixing energy can be achievedusing a high-power machine and a short residence time, or a low powermachine and a long residence time.

For an in-line static mixer, the mixing energy per unit mass can beestimated from:

${E\text{/}M} = {6.894\Delta\; p\text{/}{\rho\left\lbrack \frac{kJ}{kg} \right\rbrack}}$or${E\text{/}M} = {\frac{Pt}{\rho\; V}\left\lbrack \frac{kJ}{kg} \right\rbrack}$where (Δp) is the pressure loss (psi), ρ is density (kg/m³), P is power(kW), and t is residence time (sec).

FIG. 26A is a plot illustrating filtration ratio as a function ofspecific mixing energy for various configurations of static mixersincluding single stage mixing in yard test and field pilot test. Above0.15 kJ/kg of specific mixing energy, a filtration ratio of less than1.5 could be achieved. Below the low mixing energy (E/M<0.15 kJ/kg), FRsgreater than 1.5 began to be observed. FIG. 26B is a plot illustratingthe filtration ratio as a function of specific mixing energy for variousconfigurations of static mixers in yard tests and Lab-scale overheadmixing tests. As mentioned above, the trends in FR observed in lab-scalemixing correlate will with the trends observed in yard-scale mixing.Note that the mixing time in the laboratory was approximately 15 minutesto 24 hours, while the mixing time in yard test was less than a fewseconds in the static mixer.

FIG. 27 is a plot illustrating the viscosity as a function of specificmixing energy for single stage and dual stage mixing configurationsemploying in-line static mixers. As shown in FIG. 22 and FIG. 27, theexpected viscosity yield could be achieved when the specific mixingenergy was below 1.2 kJ/kg in the system. The viscosity dropped above1.4 kJ/kg. These results suggest that specific mixing energies between0.15 and 1.4 kJ/kg provide for both the specified viscosity with a goodfilterability (FR less than 1.5).

Calculated specific mixing energy values associated with all trials areincluded in Tables 6-9.

On-Site Injectivity Test in the Field Using a PMU:

Aqueous polymer solutions prepared using field-scale single stage mixingmethods were qualified using a PMU.

FIG. 28 shows the field core flood (CF1) using the field-preparedsamples. Neat liquid polymer composition was collected in the tank andthe inversion and dilution to 2000 ppm polymer solution was performedusing the overhead mixer in the on-site laboratory. The viscosity andfiltration ratio (FR) at 1.2 μm filter for the inverted aqueous polymersolution were found to be 22 cP and 1.24, respectively. The invertedaqueous polymer solution was injected at 0.5 mL/min into a 1.4 Dsandstone core, and the pressure drop across the whole core (6″) andinjection face (2″) were measured. The inverted aqueous polymer solutionwas prepared in the lab using neat liquid polymer. As shown in the FIG.28, no significant plugging was observed during the coreflood up to 14PV.

FIG. 29 shows another example of field core flood (CF2) performed usinga wellhead sample mixed in the field using the single stage mixingprocess described above. The neat liquid polymer was inverted anddiluted through the field inline mixer. The 1800 ppm inverted aqueouspolymer solution sample was obtained from the wellhead. The polymerflood was run at 0.5 ml/min in the sandstone core (1.4 D). As shown inFIG. 29, no significant plugging was observed up to 11 PV, even thoughit took a little more to stabilize the pressure drop relative to trialsperformed using a lab-mixed aqueous polymer solution (see FIG. 28). FIG.30 shows the filtration ratio test result at 1.2 micron under 1 bar forthe wellhead-collected sample used for the CF2 flood. The sampleexhibited very good filterability (FR of 1.09).

FIG. 31 shows the pressure drop along different flow rate to estimatethe viscosity using a capillary viscometer in a portable polymer floodbox. As shown in the box, the field samples from wellhead exhibitedcomparable viscosities above the specified viscosity of 22 cP, which wasmeasured in the laboratory as a reference. Filtration ratios of lessthan 1.5 were also observed a various different injection rates. Theseresults indicate the achievement of good filterability and viscosityyield using a single stage mixing process in the field.

Darcy Friction Factor in the Static Mixer.

Liquid polymer can also be used as a friction reducer in pipe flow. TheDarcy-Weisbach relation was used to estimate the friction reductioncharacteristic property of liquid polymer during the mixing in a staticmixer. The Darcy-Weisbach equation is a phenomenological equation, whichrelates the head loss, or pressure loss, due to friction along a givenlength of pipe to the average velocity of the fluid flow for anincompressible fluid. The Darcy-Weisbach equation contains adimensionless friction factor, known as the Darcy friction factor

$\frac{\Delta\; p}{L} = {f_{D} \cdot \frac{\rho}{2} \cdot \frac{\left\langle v \right\rangle^{2}}{D}}$where Δp, L and D is pressure drop (Pa), length (m) and Diameter (m) ofa static mixer, f_(D) is Darcy-Weisbach fraction factor, <ν> and ρ ismean flow velocity (m/s) and density (kg/m³) of fluid.

FIG. 32 shows the correlation between pressure drop and flow rate acrossthe static mixer with a diameter of 2″ and 3″ respectively. As shown inFIG. 32, pressure drop and flow rate shows a linear relationship and theslope is corresponding the Darcy-Weisbach friction factor. From theseresults, the pressure drop at different flow rates during mixing andhydration in the inline mixer can be estimated in field application.FIG. 33 shows Darcy-friction factor vs. Reynolds number. TheDarcy-friction factor in smooth pipe flow is illustrated as a baseline.As shown in FIG. 33, the Darcy-friction factor in a turbulent flow isusually calculated in the order of 0.01˜0.1 in a smooth pipe line and inthe order of 0.1˜1 in a rough pipe line (not shown in the plot).However, the Darcy-Weisbach friction factor in single step inline mixeris calculated in the order of 1˜10 in the same range of Reynolds numberdue to the presence of mixing elements in the inline mixer.

Specific Mixing Energy for Powder HPAM Polymer.

The mixing of various powder polymer to apply the specific mixing energyconcept. Various powder HPAM polymers from different vendors were mixedusing a laboratory overhead mixer set at different mixing time and rpm.The measured performance of each polymer such as filtration ratio andviscosity have been correlated with the specific mixing energy. Theresults are shown in FIGS. 34A-36B.

FIGS. 34A and 34B show the results of filtration ratio along thecalculated specific mixing energy with 5 micron and 1.2 micron filter,respectively. As shown in FIGS. 34A and 34B, most of the polymers easilypassed 5 micron filter even at low specific mixing energy while a few ofpolymers passed 1.2 micron filter at low specific mixing energy. Sincepowder polymers doesn't have any additives such as inversion surfactantwhich helps polymer hydration and mixing faster in liquid polymer, itrequires somewhat higher mixing energy than those in liquid polymer.

FIG. 35 shows the viscosity along the specific mixing energy for powderHPAM polymers. Similar with liquid polymer, powder polymer also showstendency of decreasing of its viscosity as specific mixing energyincreases, that indicates the limit of specific mixing energy tominimize the mechanical degradation of polymer during themixing/hydration process.

FIGS. 36A and 36B show the sensitivity tests for each component tocalculate the specific mixing energy such as mixing speed and mixingtime, respectively. As shown above, better filtration ratio can beachieved by increasing mixing speed and hydration time proportional tothe specific mixing energy. However, there is an operation limit of thespecific mixing energy as discussed above, that imply the operationwindows for hydration of powder polymers.

Rod-Climbing (Weissenberg Effect) During Hydration of Polymer.

Rod-climbing, so-called Weissenberg effect, is a well-known phenomenonthat shows the viscoelastic property of non-Newtonian polymer solution.This phenomenon occurs due to the normal stress difference in polymersolution as described in equation below while vortex is observed inmixing of water

$\frac{d\left( {p - \tau_{33}} \right)}{d\mspace{11mu}\ln\mspace{11mu} r} = {{{- 2}\tau_{12}\frac{d\left( {\tau_{22} - \tau_{33}} \right)}{d\;\tau_{12}}} - \left( {\tau_{11} - \tau_{22}} \right) + {\rho\; v_{1}^{2}}}$

if >0; Newtonian fluids to generate vortex,

if <0; non-Newtonian fluids (polymer solution) to generate rod-climbing

where p is pressure, r is radius, τ₁₁, τ₂₂ and τ₃₃ are normal stresstensors, τ₁₂ is shear stress tensor ν₁ is velocity of rotation.

Rod-climbing is an extension of the viscoelastic properties of a polymersolution, and depends on polymer molecular weight, concentration, brinesalinity, brine hardness, and temperature. Rod-climbing behavior can beused as a visual indicator of quick or fast hydration of liquid polymeror powder polymer. To observe the rod-climbing and hydration clearlyirrespective of the molecular weight of polymer molecules during themixing, a 1% polymer solution was prepared in a synthetic brine (seeTable 1). The rod-climbing along with hydration of polymer was observedas (1) a decrease in the surface level of vortex, and (2) increase ofrod-climbing of the polymer solution. In the case of liquid polymers andpowder polymers that show relatively quick hydration, the decrease inthe surface level of the vortex and the onset of rod-climbing occursimultaneously. Other polymers show gradual decrease in surface levelfollowed by a subsequent onset of rod-climbing. The observation ofrod-climbing and resulting characteristic performance are summarized inTable 10 for a variety of polymers.

TABLE 10 Onset of rod-climbing of liquid polymer and powder polymers.ON-SET OF HEIGHT OF ROD- ROD- CLIMBING CLIMBING (MIN) (CM, MAX) COMMENTLP #1 0.25 5 New LP, 50% active, Simultaneous rod-climbing after surfacelevel-down LP #2 3 2 Conventional, 30% active, Delay of rod-climbingafter surface level-down HPAM#1 1.5 3.5 Fast hydration ATBS-PAMterpolymer (20M), powder HPAM#2 3.5 3.5 Fast hydration HPAM (20M),powder HPAM#3 18 1.5 Delay of rod-climbing after surface level-down,powder

Polymer Mixing Systems for Use in Subsea Mixing:

Currently, there are relatively few cases worldwide where subsea polymerinjection has been employed in an Enhanced Oil Recovery (EOR)application. When conducted previously, polymer flooding solutions weremixed on the host facility and transported to the subsea wells viaindividual flowlines.

To provide polymer injection for EOR purposes, the polymer solution mustbe mixed on an offshore facility and transported on an individual basisto each of the injection wells. This increases the deck space, processand operations requirements for the host facility regardless of whetherit is a new build or existing facility. Further, polymer solutioninjection systems are reliant on individual lines from the mixers to theinjection wells. This is because traditional flow control valves areknown to degrade the polymer solution properties. As a consequence,manifold-type arrangements can be incompatible with polymer solutions.This can significantly increase the specified infrastructure required tosupport each subsea injector.

There are no known designs which relocate the polymer mixing processfrom the host facility to subsea. To address this shortcoming, polymermixing systems were developed that could be used to relocate the polymermixing process from the host platform to a subsea area in an effort toreduce the size of the host platform and the number of flowlines infield.

The polymer mixing systems allow the relocation of the mixing equipmentfrom the platform to the seabed at the subsea drill center(s). Thisallows polymer mixing to be conducted at a subsea area, not on a hostfacility.

The polymer mixing systems employ field proven equipment to control andmonitor the mixing process. Example polymer mixing systems areschematically illustrated in FIGS. 37 and 38. Each polymer mixing systemreceives two supplies. One supply is the neat polymer and the second isa separate water supply. These two products are combined in eachmanifold branch mixer arrangement in order to create the correctconcentration of polymer solution for injection into each well. Thesystem contains all mixing equipment, instrumentation, valves and otherassociated equipment to satisfactorily control and monitor the mixingprocess and to provide the polymer solution for injection at each of thesubsea wells.

The overall process design is similar for the polymer mixing systemsillustrated in FIGS. 37 and 38. However, one polymer mixing system (FIG.37) utilizes two forms of flow control, one for water and the other forneat polymer. This mixing system can be used when polymer is suppliedthrough a single conduit and manifolded to provide supply to multiplebranches; similar to that of the water supply. The second polymer mixingsystem (FIG. 38) only controls the water throughput across the system.This system can be used in cases where multiple individual conduitssupply polymer directly to each manifold branch. An appropriate polymermixing system for a particular application can be selected based onproperties of the polymer being mixed.

The polymer mixing systems receive water from the host facility via thewater flowline that is connected to the header pipe where it manifoldsout to the mixing system.

The branch pipework provides water through the piping up to the watercontrol choke valve. As this valve position varies, the amount of waterflowing through the branch is adjusted and thus controls the flowthrough the 1st stage mixer. The polymer is introduced to the water flowat the first stage mixer. The neat polymer to each branch is eitherprovided via an individual conduit such as an umbilical core or flowlinebundle (multiple feed) or is supplied via a neat polymer header andmanifolded (individual feed). In the individual feed design, there is asecond flow controlling valve on each branch which adjusts the neatpolymer flow into the process. This valve can be either a low shearingchoke valve, Chemical Injection Metering Valve (CIMV) or control valvedepending on the neat polymer properties. The water and neat polymer areintroduced at the first stage mixer, this is the initial point at whichthe solution formulates. The flow is then passed through the 2nd stagemixer where the mixing process is completed and the solution is readyfor injection.

By relocating the polymer mixing from the host to a subsea location, asignificant reduction in equipment sited on the host as well as asignificant reduction in supporting subsea infrastructure can beachieved.

For example, by employing a polymer mixing system, the subsea flowlineinfrastructure associated with hydrocarbon recover can be reduced byaround 50 to 60%. This will improve overall project expenditure,scheduling and exposure during installation and operation. Therelocation of the mixing equipment from the host platform to the subseaarea(s) will also allow a number of risers to be removed from theplatform design and all associated mixing equipment. These systems mayalso obviate the need for new platforms in some settings.

The compositions and methods of the appended claims are not limited inscope by the specific compositions and methods described herein, whichare intended as illustrations of a few aspects of the claims. Anycompositions and methods that are functionally equivalent are intendedto fall within the scope of the claims. Various modifications of thecompositions and methods in addition to those shown and described hereinare intended to fall within the scope of the appended claims. Further,while only certain representative compositions and method stepsdisclosed herein are specifically described, other combinations of thecompositions and method steps also are intended to fall within the scopeof the appended claims, even if not specifically recited. Thus, acombination of steps, elements, components, or constituents may beexplicitly mentioned herein or less, however, other combinations ofsteps, elements, components, and constituents are included, even thoughnot explicitly stated.

The term “comprising” and variations thereof as used herein is usedsynonymously with the term “including” and variations thereof and areopen, non-limiting terms. Although the terms “comprising” and“including” have been used herein to describe various embodiments, theterms “consisting essentially of” and “consisting of” can be used inplace of “comprising” and “including” to provide for more specificembodiments of the invention and are also disclosed. Other than wherenoted, all numbers expressing geometries, dimensions, and so forth usedin the specification and claims are to be understood at the very least,and not as an attempt to limit the application of the doctrine ofequivalents to the scope of the claims, to be construed in light of thenumber of significant digits and ordinary rounding approaches.

It is understood that when combinations, subsets, groups, etc. ofelements are disclosed (e.g., combinations of components in acomposition, or combinations of steps in a method), that while specificreference of each of the various individual and collective combinationsand permutations of these elements may not be explicitly disclosed, eachis specifically contemplated and described herein. By way of example, ifa composition is described herein as including a component of type A, acomponent of type B, a component of type C, or any combination thereof,it is understood that this phrase describes all of the variousindividual and collective combinations and permutations of thesecomponents. For example, in some embodiments, the composition describedby this phrase could include only a component of type A. In someembodiments, the composition described by this phrase could include onlya component of type B. In some embodiments, the composition described bythis phrase could include only a component of type C. In someembodiments, the composition described by this phrase could include acomponent of type A and a component of type B. In some embodiments, thecomposition described by this phrase could include a component of type Aand a component of type C. In some embodiments, the compositiondescribed by this phrase could include a component of type B and acomponent of type C. In some embodiments, the composition described bythis phrase could include a component of type A, a component of type B,and a component of type C. In some embodiments, the compositiondescribed by this phrase could include two or more components of type A(e.g., A1 and A2). In some embodiments, the composition described bythis phrase could include two or more components of type B (e.g., B1 andB2). In some embodiments, the composition described by this phrase couldinclude two or more components of type C (e.g., C1 and C2). In someembodiments, the composition described by this phrase could include twoor more of a first component (e.g., two or more components of type A (A1and A2)), optionally one or more of a second component (e.g., optionallyone or more components of type B), and optionally one or more of a thirdcomponent (e.g., optionally one or more components of type C). In someembodiments, the composition described by this phrase could include twoor more of a first component (e.g., two or more components of type B (B1and B2)), optionally one or more of a second component (e.g., optionallyone or more components of type A), and optionally one or more of a thirdcomponent (e.g., optionally one or more components of type C). In someembodiments, the composition described by this phrase could include twoor more of a first component (e.g., two or more components of type C (C1and C2)), optionally one or more of a second component (e.g., optionallyone or more components of type A), and optionally one or more of a thirdcomponent (e.g., optionally one or more components of type B).

Unless defined otherwise, all technical and scientific terms used hereinhave the same meanings as commonly understood by one of skill in the artto which the disclosed invention belongs. Publications cited herein andthe materials for which they are cited are specifically incorporated byreference.

What is claimed is:
 1. A method for preparing an aqueous polymersolution, the method comprising: (i) providing a liquid polymer (LP)composition comprising one or more synthetic (co)polymers; and (ii)combining the LP composition with an aqueous fluid in a single stagemixing process to provide the aqueous polymer solution, wherein thesingle stage mixing process comprises applying a specific mixing energyof at least 0.10 kJ/kg to the LP composition and the aqueous fluid;wherein the aqueous polymer solution comprises a concentration ofsynthetic (co)polymer of from 50 to 15,000 ppm; and wherein the aqueouspolymer solution has a filter ratio of 1.5 or less at 15 psi using a 1.2μm filter.
 2. The method of claim 1, wherein the LP compositioncomprises: one or more hydrophobic liquids having a boiling point of atleast 100° C.; at least 39% by weight of the one or more synthetic(co)polymers; one or more emulsifier surfactants; and one or moreinverting surfactants.
 3. The method of claim 1, wherein the LPcomposition is in the form of an inverse emulsion comprising: one ormore hydrophobic liquids having a boiling point of at least 100° C.; upto 38% by weight of one or more synthetic (co)polymers; one or moreemulsifier surfactants; and one or more inverting surfactants.
 4. Themethod of claim 1, wherein the LP composition comprises a substantiallyanhydrous polymer suspension, the substantially anhydrous polymersuspension comprising a powder polymer having an average molecularweight of from 0.5 to 30 million Daltons suspended in a carrier havingan HLB of greater than or equal to 8, wherein the carrier comprises oneor more surfactants, and wherein the powder polymer and the carrier arepresent in the substantially anhydrous polymer suspension at a weightratio of from 20:80 to 80:20.
 5. The method of claim 1, wherein theaqueous polymer solution has a filter ratio of from 1.1 to 1.3 at 15 psiusing the 1.2 μm filter.
 6. The method of claim 1, wherein step (ii)comprises a continuous process.
 7. The method of claim 1, wherein thesingle stage mixing process comprises a single mixing step, wherein thesingle mixing step comprises passing the LP composition and the aqueousfluid through an in-line mixer having a mixer inlet and a mixer outletto provide the aqueous polymer solution.
 8. The method of claim 1,wherein the single stage mixing process comprises multiple mixing steps,wherein the single stage mixing process comprises as a first mixingstep, passing the LP polymer composition and the aqueous fluid through afirst in-line mixer having a first mixer inlet and a first mixer outletto provide a partially mixed aqueous polymer solution; and as a secondstep, passing the partially mixed aqueous polymer solution through asecond in-line mixer having a second mixer inlet and a second mixeroutlet to provide the aqueous polymer solution.
 9. The method of claim1, wherein the single stage mixing process comprises parallel singlemixing steps.
 10. The method of claim 9, wherein the parallel singlemixing steps comprise combining the LP composition with the aqueousfluid in a polymer mixing system, wherein the polymer mixing systemcomprises: (i) a main polymer feed line diverging to a plurality ofpolymer supply branches, (ii) a main aqueous feed line diverging to aplurality of aqueous supply branches, (iii) a plurality of mixerarrangements, each of which comprises an in-line mixer having a mixerinlet and a mixer outlet; wherein each of the plurality of mixerarrangements is supplied by one of the plurality of polymer supplybranches and one of the plurality of aqueous supply branches; andwherein combining the LP composition with an aqueous fluid in a polymermixing system comprises (a) passing the LP polymer composition throughthe main polymer feed line and the plurality of polymer supply branchesto reach each of the plurality of mixer arrangements; (b) passing theaqueous fluid through the main aqueous feed line and the plurality ofaqueous supply branches to reach each of the plurality of mixerarrangements; wherein the LP polymer composition and the aqueous fluidflow through the in-line mixer of each of the plurality of mixerarrangements to provide the aqueous polymer solution.
 11. The method ofclaim 10, wherein the main polymer feed line is fluidly connected to theplurality of polymer supply branches via a polymer distributionmanifold, wherein the polymer distribution manifold independentlycontrols the fluid flow rate through each of the plurality of polymersupply branches.
 12. The method of claim 10, wherein the mixing systemis positioned subsea.
 13. The method of claim 1, wherein the singlestage mixing process comprises parallel multiple mixing steps.
 14. Themethod of claim 13, wherein the parallel multiple mixing steps comprisecombining the LP composition with the aqueous fluid in a polymer mixingsystem, wherein the polymer mixing system comprises: (i) a main polymerfeed line diverging to a plurality of polymer supply branches, (ii) amain aqueous feed line diverging to a plurality of aqueous supplybranches, (iii) a plurality of mixer arrangements, each of whichcomprises a first in-line mixer having a first mixer inlet and a firstmixer outlet in series with a second in-line mixer having a second mixerinlet and a second mixer outlet; wherein each of the plurality of mixerarrangements is supplied by one of the plurality of polymer supplybranches and one of the plurality of aqueous supply branches; andwherein combining the LP composition with an aqueous fluid in a polymermixing system comprises (a) passing the LP composition through the mainpolymer feed line and the plurality of polymer supply branches to reacheach of the plurality of mixer arrangements; (b) passing the aqueousfluid through the main aqueous feed line and the plurality of aqueoussupply branches to reach each of the plurality of mixer arrangements;wherein the LP composition and the aqueous fluid flow through the firstin-line mixer of each of the plurality of mixer arrangements to providea partially mixed aqueous polymer solution, and then the partially mixedaqueous polymer solution flows through the second in-line mixer of eachof the plurality of mixer arrangements to provide the aqueous polymersolution.
 15. The method of claim 14, wherein the main polymer feed lineis fluidly connected to the plurality of polymer supply branches via apolymer distribution manifold, wherein the polymer distribution manifoldindependently controls the fluid flow rate through each of the pluralityof polymer supply branches.
 16. The method of claim 14, wherein themixing system is positioned subsea.
 17. The method of claim 1, whereinthe single stage mixing process comprises applying a specific mixingenergy of from 0.10 kJ/kg to 1.50 kJ/kg to the LP composition and theaqueous fluid.
 18. The method of claim 1, wherein the aqueous fluidfurther comprises a surfactant, an alkalinity agent, a co-solvent, achelating agent, or any combination thereof.
 19. The method of claim 1,wherein the one or more synthetic (co)polymers comprise one or moreacrylamide (co)polymers.
 20. A method for hydrocarbon recovery,comprising: (a) providing a subsurface reservoir containing hydrocarbonsthere within; (b) providing a wellbore in fluid communication with thesubsurface reservoir; (c) preparing an aqueous polymer solutionaccording to the method of claim 1; and (d) injecting the aqueouspolymer solution through the wellbore into the subsurface reservoir. 21.A method for preparing an aqueous polymer solution, the methodcomprising combining a solid powder polymer with an aqueous fluid in amixing process to provide the aqueous polymer solution, wherein themixing process comprises applying a specific mixing energy of at least1.0 kJ/kg to the solid powder polymer and the aqueous fluid; wherein theaqueous polymer solution comprises a concentration of polymer of from 50to 15,000 ppm; and wherein the aqueous polymer solution has a filterratio of 1.5 or less at 15 psi using a 1.2 μm filter.